Re: Software raid VS hardware raid
My other concern is what happens when one drive goes down if we use gmirror? Is it completelly transparent and bad drive can be hot swapped while server is running and rebuild started? I am thinking now about gpt+gmirror (including boot and swap) Artem Yes. In fact, you can test this by unplugging the data or power cable to a drive while the server is running. I've done this with consumer sata drives and, so far, not had a problem. The server stays up and running and disk access is not interrupted. I can then plug in a new disk and add it to the gmirror and the array rebuilds. I've not tried this with gpt, so I can't comment there. -Modulok- ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
30.01.2013 1:01, Warren Block: On Tue, 29 Jan 2013, Artem Kuchin wrote: 29.01.2013 18:57, Warren Block: On Tue, 29 Jan 2013, Artem Kuchin wrote: The Handbook chapter on gmirror talks about the problems with GPT and GEOM metadata. In short: right now, they conflict. It's possible to mirror GPT partitions, but be aware that if you mirror more than one partition on a drive, a rebuild after replacing a drive could thrash the heads as mirrors are rebuilt simultaneously. http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html So, gmirror+GPT=conflict on last sector GPT+gmirror = hardrive head kill nice... So, for no more than 2TB disks the best way to go is GMIRROR of the drive +PARTITION on top of it? GPT partitions should work, just limit it to one mirrored partition per drive. Please, clarify what you mean here. Or maybe there is a way to instruct gmirror do rebuild only what i say (manual rebuild) ? 'gmirror configure -n' ? Have not tried it. The trick would be to do that before multiple mirrors start rebuilding, which they will as soon as geom_mirror.ko is loaded. As i understand from the man page -n setup the device not to auto rebuild ever. So, this is probably the thing i want. I need to setup a test system and play with it a bit. Artem ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
On 01/28/13 21:43, Artem Kuchin wrote: I am planning to use mirror configuration of two SATA 7200rpm 2TB disks. I personally vote for gmirror in this case; I've used it a lot and found it very good wrt to both performance and robustness. You can spend the extra money you spare on the controller buying good disks; as someone else pointed out don't get desktop-class ones, but 24x7 ones. Just my 2c. bye av. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
30.01.2013 18:06, Warren Block: On Wed, 30 Jan 2013, Artem Kuchin wrote: 30.01.2013 1:01, Warren Block: On Tue, 29 Jan 2013, Artem Kuchin wrote: 29.01.2013 18:57, Warren Block: On Tue, 29 Jan 2013, Artem Kuchin wrote: The Handbook chapter on gmirror talks about the problems with GPT and GEOM metadata. In short: right now, they conflict. It's possible to mirror GPT partitions, but be aware that if you mirror more than one partition on a drive, a rebuild after replacing a drive could thrash the heads as mirrors are rebuilt simultaneously. http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html So, gmirror+GPT=conflict on last sector GPT+gmirror = hardrive head kill nice... So, for no more than 2TB disks the best way to go is GMIRROR of the drive +PARTITION on top of it? GPT partitions should work, just limit it to one mirrored partition per drive. Please, clarify what you mean here. If only one GPT partition on a drive is mirrored with another GPT partition on another drive, head contention never comes up. There is only one mirror. It does nearly eliminate the usefulness of GPT partitioning. Um... and how can i do that if i have a simple mirror with two drives and want to mirror everything on them? As i understand i will have at least bootable, swap and ufs parttions on those drives, that is 3 partitions at least. Artem ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
On Jan 30, 2013, at 8:10 AM, Andrea Venturoli wrote: You can spend the extra money you spare on the controller buying good disks; as someone else pointed out don't get desktop-class ones, but 24x7 ones. Server Class drives buy you some improvement, but my recent experience with Seagate Barracuda ES.2 drives is not that good. I have had 50% of them fail within the 5-year warranty period. My disks run 24x7 and I use ZFS under FreeBSD 9 so I have not lost any data. I have: 2 x Seagate ES.2 250 GB (one has failed) 4 x Seagate ES.2 1 TB (two have failed) 2 x Hitachi UltraStar 1 TB (pre-WD acquisition), no failures, but they are less than 2 years old. They are also noticeably faster than the Seagate ES.2 I just ordered 2 x WD RE4 500 GB, we'll see how those do I go out of my way to purchase disks with a 5-year warranty, they are still out there but you have to look for them. -- Paul Kraus Deputy Technical Director, LoneStarCon 3 Sound Coordinator, Schenectady Light Opera Company ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
There seems to be one more advantage to gmirror If i understood correctly gmirror label -v -b split -s 2048 data da0 da1 da2 will create a tripple mirror raid 1, that is triple redundancy, which is hardly available on any hardware raid. Am i correct here? Also, does anyone know how to choose split threshold (-s 2048) correctly ? Artem ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
On Wed, 30 Jan 2013, Artem Kuchin wrote: 30.01.2013 18:06, Warren Block: GPT partitions should work, just limit it to one mirrored partition per drive. Please, clarify what you mean here. If only one GPT partition on a drive is mirrored with another GPT partition on another drive, head contention never comes up. There is only one mirror. It does nearly eliminate the usefulness of GPT partitioning. Um... and how can i do that if i have a simple mirror with two drives and want to mirror everything on them? As i understand i will have at least bootable, swap and ufs parttions on those drives, that is 3 partitions at least. If you want to use the same drive for booting, it's possible. Create all three partitions on both drives manually. Then mirror the freebsd-ufs partition only. The contents of the freebsd-boot partition don't change often, and swap does not have to be mirrored. Not that it's easy or convenient, but it's an option. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
On Jan 30, 2013, at 10:22 AM, Warren Block wrote: If you want to use the same drive for booting, it's possible. Create all three partitions on both drives manually. Then mirror the freebsd-ufs partition only. The contents of the freebsd-boot partition don't change often, and swap does not have to be mirrored. Note that if you do NOT mirror SWAP, then in the event of a disk failure you will most likely crash when the system tries to swap in some data from the failed drive. If you mirror swap then you do not risk a crash due to missing swap data. -- Paul Kraus Deputy Technical Director, LoneStarCon 3 Sound Coordinator, Schenectady Light Opera Company ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
30.01.2013 19:28, Paul Kraus: On Jan 30, 2013, at 10:22 AM, Warren Block wrote: If you want to use the same drive for booting, it's possible. Create all three partitions on both drives manually. Then mirror the freebsd-ufs partition only. The contents of the freebsd-boot partition don't change often, and swap does not have to be mirrored. Note that if you do NOT mirror SWAP, then in the event of a disk failure you will most likely crash when the system tries to swap in some data from the failed drive. If you mirror swap then you do not risk a crash due to missing swap data. yes, that's what i wanted to say. Also, not being able to boot if first disk has some error in boot section or just strangly dead is not an option too. However, i was just thinking, if i use gmirror then bios does not know anything about it. I may set both harddisk as boot disk, but if first disk is brain damaged then bios may just stuck trying to boot from it and will not pass boot attempt to the second disk. I don't know, it depends on bios of course. But this seems to be a disadvantage to a software raid. Artem ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
On Wed, 30 Jan 2013, Artem Kuchin wrote: Also, not being able to boot if first disk has some error in boot section or just strangly dead is not an option too. However, i was just thinking, if i use gmirror then bios does not know anything about it. I may set both harddisk as boot disk, but if first disk is brain damaged then bios may just stuck trying to boot from it and will not pass boot attempt to the second disk. I don't know, it depends on bios of course. But this seems to be a disadvantage to a software raid. That's true. The similar situation with hardware RAID is when the controller fails. The metadata is probably specific to that manufacturer and maybe to that model of controller. It's a good idea to get spares, because as Murphy is my witness, in an emergency that controller will not be available in the same town, district, country, or continent. More likely it will have been long discontinued, with no data migration path. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
29.01.2013 11:54, Michael Powell: Artem Kuchin wrote: I guess what I'm trying to point out is that low performance wrt software RAID will stem from other things besides just simply consuming a few CPU cycles. Today's CPUs have the cycles to spare. I've been using gmirror for RAID 1 mirrors for a few years now and am happy with this. I have had a few old drives die and the servers stayed up and online. This allowed me to defer the actual drive replacement and not have to drop everything and fight fire. Thank you everyone for replying. I realize that many other things affect the performance, not only the CPU power. For example, disk IO kernel multithreading is one of the things. But i guess in FBSD 9 it is more or less solved. The server is going to be a web server with many sites and with mysql running on it. Nothing really really heavy. Currently with run all this on our own server with 8 cores and 16GB ram and 3ware raid1 and cpu load is about 5% :) Everything is quick and responsive. I hope to see the same on a software raid. I really don't want to deploy ZFS on a new server where all these site need to migrate because i am kind of don't fix it if it is not broken kind of guy. UFS+journaling+softupdates served us well for years and snapshots are available on ufs too. My other concern is what happens when one drive goes down if we use gmirror? Is it completelly transparent and bad drive can be hot swapped while server is running and rebuild started? I am thinking now about gpt+gmirror (including boot and swap) Artem ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
Artem Kuchin wrote: [snip] The server is going to be a web server with many sites and with mysql running on it. Nothing really really heavy. Currently with run all this on our own server with 8 cores and 16GB ram and 3ware raid1 and cpu load is about 5% :) Everything is quick and responsive. I hope to see the same on a software raid. The controller would be a slight concern. But for what you've described doing I doubt it will be a big deal. The 3Ware may have a faster processor on it than say a generic onboard built-in. But since all we're talking here is a RAID 1 mirror my guess is it may not be a big enough difference to see. Writes will be just as if you are writing to 1 drive, reads will be faster. Maybe that 5% cpu load turns into 6% or 7%. I really don't want to deploy ZFS on a new server where all these site need to migrate because i am kind of don't fix it if it is not broken kind of guy. UFS+journaling+softupdates served us well for years and snapshots are available on ufs too. I understand; I've only played around with ZFS some on Solaris. I may move in that direction some day, but for now My other concern is what happens when one drive goes down if we use gmirror? Is it completelly transparent and bad drive can be hot swapped while server is running and rebuild started? I am thinking now about gpt+gmirror (including boot and swap) I've never actually hot-swapped one but I can't see any reason why not. You can't use the gmirror remove directive when a drive has failed, but you do a gmirror forget device , swap it, then just do gmirror insert device to insert the replaced drive into the mirror. When everything is working as it should gmirror is mostly 'automatic', e.g. after the insert the rebuild just starts. Main thing I appreciated about this is the server stayed up and online after one drive died. My two servers at home are my testbeds to test out things first before doing stuff to the ones at work. I just installed both to 9.1. The difference now is I've used GPT (gpart) and this is new to me. Previously everything was always fdisk and disklabel. Both these machines are setup on one drive at this point and I haven't yet gotten into the mirroring yet. With the old fdisk/disklabel it was simple to just mirror the entire drive itself (slice). The other approach is to mirror partitions. I think I may need to do this as I think this is the way you have to proceed in order to avoid having gpt and gmirror both trying to claim the last sector on the drive (metadata storage). -Mike ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
On Tue, 29 Jan 2013, Artem Kuchin wrote: My other concern is what happens when one drive goes down if we use gmirror? Is it completelly transparent and bad drive can be hot swapped while server is running and rebuild started? I am thinking now about gpt+gmirror (including boot and swap) As far a gmirror is concerned, yes, drives can be removed and new drives inserted while the mirror is running. Hot swap is more of an issue with the hardware. I have not tried it with SATA drives, although I think it should work. The Handbook chapter on gmirror talks about the problems with GPT and GEOM metadata. In short: right now, they conflict. It's possible to mirror GPT partitions, but be aware that if you mirror more than one partition on a drive, a rebuild after replacing a drive could thrash the heads as mirrors are rebuilt simultaneously. http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
29.01.2013 18:57, Warren Block: On Tue, 29 Jan 2013, Artem Kuchin wrote: The Handbook chapter on gmirror talks about the problems with GPT and GEOM metadata. In short: right now, they conflict. It's possible to mirror GPT partitions, but be aware that if you mirror more than one partition on a drive, a rebuild after replacing a drive could thrash the heads as mirrors are rebuilt simultaneously. http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html So, gmirror+GPT=conflict on last sector GPT+gmirror = hardrive head kill nice... So, for no more than 2TB disks the best way to go is GMIRROR of the drive +PARTITION on top of it? Or maybe there is a way to instruct gmirror do rebuild only what i say (manual rebuild) ? Artem ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
On Tue, 29 Jan 2013 08:57:31 -0600, Warren Block wbl...@wonkity.com wrote: As far a gmirror is concerned, yes, drives can be removed and new drives inserted while the mirror is running. Hot swap is more of an issue with the hardware. I have not tried it with SATA drives, although I think it should work. The Handbook chapter on gmirror talks about the problems with GPT and GEOM metadata. In short: right now, they conflict. It's possible to mirror GPT partitions, but be aware that if you mirror more than one partition on a drive, a rebuild after replacing a drive could thrash the heads as mirrors are rebuilt simultaneously. http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html Why isn't gmirror more intelligent? I hate to use Linux as an example, but mdadm won't simultaneously rebuild multiple RAID sets if they use the same physical providers to prevent this. Could this be added as a feature? Even a sysctl toggle? ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
On Tue, 29 Jan 2013, Artem Kuchin wrote: 29.01.2013 18:57, Warren Block: On Tue, 29 Jan 2013, Artem Kuchin wrote: The Handbook chapter on gmirror talks about the problems with GPT and GEOM metadata. In short: right now, they conflict. It's possible to mirror GPT partitions, but be aware that if you mirror more than one partition on a drive, a rebuild after replacing a drive could thrash the heads as mirrors are rebuilt simultaneously. http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html So, gmirror+GPT=conflict on last sector GPT+gmirror = hardrive head kill nice... So, for no more than 2TB disks the best way to go is GMIRROR of the drive +PARTITION on top of it? GPT partitions should work, just limit it to one mirrored partition per drive. Or maybe there is a way to instruct gmirror do rebuild only what i say (manual rebuild) ? 'gmirror configure -n' ? Have not tried it. The trick would be to do that before multiple mirrors start rebuilding, which they will as soon as geom_mirror.ko is loaded. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Software raid VS hardware raid
Hello! I have to made a decision on choosing a dedicated server. The problem i see is that while i can find very affordable and good options they do not provide hardware raid or even if they do it is not the best hardware for freebsd. The server base conf is 8core 32gb ram 2.8+ ghz. So, maybe someone has personal experience with both worlds and can tell if it really matters in such configuration if i go for software raid. What are the benefits and what are the negatives of software raid? How much is the performance penalty? I am planning to use mirror configuration of two SATA 7200rpm 2TB disks. Nothing fancy. File system planned is UFS with journaling. Artem ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
On 01/28/13 21:43, Artem Kuchin wrote: Hello! I have to made a decision on choosing a dedicated server. The problem i see is that while i can find very affordable and good options they do not provide hardware raid or even if they do it is not the best hardware for freebsd. The server base conf is 8core 32gb ram 2.8+ ghz. So, maybe someone has personal experience with both worlds and can tell if it really matters in such configuration if i go for software raid. What are the benefits and what are the negatives of software raid? How much is the performance penalty? I am planning to use mirror configuration of two SATA 7200rpm 2TB disks. Nothing fancy. File system planned is UFS with journaling. I won't delve into detail here but if the data is important HW RAID is where you want to be. Perhaps you could give us a little more details about what the purpose of the server is? Mission-critical or low cost? Those two tends to be mutually exclusive... We are HP-only but have good experience from LSI as well. Just my $0.02. //per ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
On Mon, 28 Jan 2013, Per olof Ljungmark wrote: On 01/28/13 21:43, Artem Kuchin wrote: Hello! I have to made a decision on choosing a dedicated server. The problem i see is that while i can find very affordable and good options they do not provide hardware raid or even if they do it is not the best hardware for freebsd. The server base conf is 8core 32gb ram 2.8+ ghz. So, maybe someone has personal experience with both worlds and can tell if it really matters in such configuration if i go for software raid. What are the benefits and what are the negatives of software raid? How much is the performance penalty? I am planning to use mirror configuration of two SATA 7200rpm 2TB disks. Nothing fancy. File system planned is UFS with journaling. I won't delve into detail here but if the data is important HW RAID is where you want to be. Perhaps you could give us a little more details A problem with HW RAID is that if the controller breaks, you need to get an identical controller to replace it, or the data will be lost. With software raid, you can read the data on any machine that will boot FreeBSD. That is a great convenience compared to searching eBay for an obsolete controller with the proper rev level. We haven't noticed any speed disadvantage on modern multi-core hardware and RAID 1. The advantages of HW raid escape me - I understand that years ago it provided OS independence and reduced CPU load, but it no longer provides the former, and with 8 cores do you need the latter while waiting for a disk platter to spin? ZFS is worthwhile, too, especially since you have a good amount of memory. That would give you snapshots and some other desirable features, such as background scanning for defects that UFS doesn't have. about what the purpose of the server is? Mission-critical or low cost? Those two tends to be mutually exclusive... Surely the presence of SATA drives shows that low cost is essential. Mirroring and ZFS provide very important advantages. HW raid seems to fill a much needed gap (apologies to Brian Kernigan). daniel feenberg We are HP-only but have good experience from LSI as well. Just my $0.02. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
On Jan 28, 2013, at 3:43 PM, Artem Kuchin wrote: I have to made a decision on choosing a dedicated server. The problem i see is that while i can find very affordable and good options they do not provide hardware raid or even if they do it is not the best hardware for freebsd. I prefer SW RAID, specifically ZFS, for two very large reasons: 1) Visibility: From the OS layer you have very good visibility into the health of the RAID set and the underlying drives. All of the lower end HW RAID solutions I have seen require proprietary software to manage the RAID configuration, usually from the physical system's BIOS layer. Finding good OS layer software to monitor the RAID and the drives has been very painful. If you don't know you have a failure, then you can't do anything about it and when you have a second failure you lose data. Running a HW RAID system and not being able to issue a simple command from the OS and see the status of the RAID scares me. 2) Error Detection and Correction: HW RAID relies on the drives to report read and write errors. With UNCORRECTABLE error rates of 10^-14 and 10^-15 and LARGE (1 TB plus) drives you are almost guaranteed to statistically run into UNCORRECTABLE errors over the life of a typical drive. ZFS has end to end checksums and can detect a single bad bit from a drive, if the set is redundant it can recreate the correct data and re-write it, effectively correcting the bad data on disk. NOTE: Larger, more expensive HW RAID systems address both of the above issues, but at a much higher cost in terms of money and management overhead. DISCLAIMER: I have been managing mission critical, cannot afford to lose it data under ZFS for over 5 years, with no loss of data (even with some horribly unreliable low cost HW RAID systems under the ZFS layer... if we had not used ZFS we would have lost data multiple times). -- Paul Kraus Deputy Technical Director, LoneStarCon 3 Sound Coordinator, Schenectady Light Opera Company ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Software raid VS hardware raid
Artem Kuchin wrote: Hello! I have to made a decision on choosing a dedicated server. The problem i see is that while i can find very affordable and good options they do not provide hardware raid or even if they do it is not the best hardware for freebsd. The server base conf is 8core 32gb ram 2.8+ ghz. So, maybe someone has personal experience with both worlds and can tell if it really matters in such configuration if i go for software raid. What are the benefits and what are the negatives of software raid? How much is the performance penalty? I am planning to use mirror configuration of two SATA 7200rpm 2TB disks. Nothing fancy. File system planned is UFS with journaling. I can't say for sure exactly what's best for your needs, however, please allow me to toss out some very generic tidbits which may aid you in some way. Historically back when RAID was new, hardware controllers were the only way to go. Back then I would never look at software RAID for a server machine. Best to offload as much work away from the CPU as possible to free it up for running the OS. What has changed is the amount of raw horsepower available from modern-day processors as compared to when RAID first came out. On the multi-core monster CPUs of today software RAID is a perfectly viable consideration because there are CPU cycles to spare, so the performance penalty is less now than it once was. Having said that, there are several other considerations to keep in mind as well. The type of RAID required matters. If you want/need RAID 5/6 it is definitely better to go with hardware RAID because of the horsepower required to do the XOR parity generation. You would want RAID 5/6 running on a hardware controller and not on the CPU. On the other hand, RAID 0, 1, and 10 are fine candidates for software RAID. One thing I've noticed that seems to somewhat get lost in this discussion is equating software-based RAID with not needing to spend money on the expensive RAID controller. At first glance it does seem like quite a waste to spend hundreds of dollars on a really fast RAID controller and then turn all its functionality off and just use it JBOD style. If you truly want performance you still need the processing power of the hardware chip on the (expensive) controller. Most central to this is I/Os per second. This matters more to some workloads than others, with being a database server probably at the top of the list where I/Os per second is king. The better the chip on the controller card the more I/Os per second. Another thing that matters less wrt to server hardware is the third kind of RAID known as fake or pseudo RAID. This is mostly found on desktop PC motherboards and some low-end (cheap) hardware cards. There is a config in the BIOS to set up so-called RAID, but it is only half of the matter - the other half is in the driver. FreeBSD does indeed have support for some of these fake RAID things but I stay far far away from them. Either go hardware or pure software only - the fakeraid is crap. Another thing I'd warn you about is the drives themselves. Take a look: http://wdc.custhelp.com/app/answers/detail/a_id/1397 Many people get very lucky much of the time and don't experience problems with this. Using drives designed for desktop PCs with RAID can be prone to problem. Drives designed for servers are more expensive, but I've always felt it is better to put server drives in servers. :-) In terms of a 'performance penalty' what you will find is it gets shifted away from just losing a few CPU cycles into other areas. If the drives are Advanced Format 4k sector critters and they aren't properly aligned in the partitioning phase of set up performance will take a hit. If the controller chip they are hooked up to is slow, then the entire drive subsystem will suffer. Another thing you will find that will surface as a problem area is the shift away from the old style DOS MBR scheme and towards GPT. Software RAID (and indeed hardware controllers too) store their metadata at the end of the drive and needs to be outside the file system. The problem arises when both the software raid and the GPT partitioning try to store metadata to the same location and collide. Just knowing about this in advance and spending some quality reading time about it prior to trying to set up the box will help greatly. Plenty has been written (even in this list) about this subject by people smarter than me so the info you need is out there, albeit it can be confusing at first. I guess what I'm trying to point out is that low performance wrt software RAID will stem from other things besides just simply consuming a few CPU cycles. Today's CPUs have the cycles to spare. I've been using gmirror for RAID 1 mirrors for a few years now and am happy with this. I have had a few old drives die and the servers stayed up and online. This allowed me to defer the actual drive replacement and not have
