Re: FreeBSD Preferred RAID controllers
--- On Sat, 2/14/09, Gabe n...@att.net wrote: From: Gabe n...@att.net Subject: Re: FreeBSD Preferred RAID controllers To: Matthew Seaman m.sea...@infracaninophile.co.uk Cc: freebsd-questions@freebsd.org Date: Saturday, February 14, 2009, 8:41 PM --- On Sat, 2/14/09, Matthew Seaman m.sea...@infracaninophile.co.uk wrote: From: Matthew Seaman m.sea...@infracaninophile.co.uk Subject: Re: FreeBSD Preferred RAID controllers To: n...@att.net Cc: freebsd-questions@freebsd.org Date: Saturday, February 14, 2009, 8:30 AM Gabe wrote: --- On Mon, 2/9/09, Matthew Seaman m.sea...@infracaninophile.co.uk wrote: From: Matthew Seaman m.sea...@infracaninophile.co.uk Subject: Re: FreeBSD Preferred RAID controllers To: n...@att.net Cc: freebsd-questions@freebsd.org Date: Monday, February 9, 2009, 3:08 PM Gabe wrote: Now with a gstripe+gmirror setup, would it be possible to fail a specific drive on purpose? I mean fail a (good) drive, pull it out, replace it and rebuild(?) it. I know I know, but humor me. Yes. Cheers, Matthew Well, to 'fail' the drive, you'ld have to physically pull the drive from the chassis which will involve a power cycle unless you've got hot-swap drives. Of course, you should confirm that your system will boot with the RAID in a degraded state and that rebuilding the RAID will continue even if interrupted by a reboot. gmirror(8) passes those tests. You do have to type some commands to get a mirror to rebuild (examples are shown in the man page) unlike some hardware RAIDs where simply inserting an unused disk is sufficient. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW Hello again all, So I wanted to test out gmirror on software RAID so I installed a completely vanilla FBSD 7, as base an install as you can get, it hasn't even been on the network. Anyway, I did the following upon first boot to get gmirror going: # sysctl kern.geom.debugflags=17 Then: # gmirror label -vb round-robin gm0 /dev/ad0 Then: # gmirror load Then: # echo 'geom_mirror_load=YES' /boot/loader.conf Then I edited /etc/fstab to show: /dev/mirror/gm0s1bnoneswapsw 0 0 /dev/mirror/gm0s1a/ ufs rw 1 1 /dev/mirror/gm0s1e/tmpufs rw 0 0 /dev/mirror/gm0s1f/usrufs rw 2 2 /dev/mirror/gm0s1d/varufs rw 2 2 I then rebooted the system, once I setup the mirror: # gmirror insert gm0 /dev/ad1 # gmirror status and it shows as COMPLETE. Okay, here comes the annoying part, I've got hot-swappable bays and I went ahead and pulled the drive. I then tried to write to the disk so that it realizes the disk is no longer there: # touch file once I do that and execute: gmirror status it shows as degraded. All fine and dandy. However when it comes time to pop the drive back in the drive is not recognized at all. I mean, the green light on the bay comes on so it definitely makes a connection but then thats it, atacontrol list doesn't list it and gmirror status still shows the same, degraded. What gives? I wonder if this is hardware related? Bios related even? Any clues? See atacontrol(8) # atacontrol list shows what your system knows is there # atacontrol attach X where X is the channel number, probes and attaches any devices on that channel in exactly the same way it is done at system boot. See camcontrol(8) if you've got SCSI drives. Cheers, Matthew -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW They're SATA drives. The two drives are on the same channel when using atacontrol list. I'm unsure that atacontrol attach ata0 would work but I'll give it a shot, hopefully that works. I'll report back. Thanks again No go. atacontrol attach ata0 fails with Device exists probably because both sata drives are on the same channel. Still though, once inserted the kernel should show that it was inserted in /var/log/messages
Re: FreeBSD Preferred RAID controllers
--- On Sat, 2/14/09, Gabe n...@att.net wrote: From: Gabe n...@att.net Subject: Re: FreeBSD Preferred RAID controllers To: Matthew Seaman m.sea...@infracaninophile.co.uk Cc: freebsd-questions@freebsd.org Date: Saturday, February 14, 2009, 8:41 PM --- On Sat, 2/14/09, Matthew Seaman m.sea...@infracaninophile.co.uk wrote: From: Matthew Seaman m.sea...@infracaninophile.co.uk Subject: Re: FreeBSD Preferred RAID controllers To: n...@att.net Cc: freebsd-questions@freebsd.org Date: Saturday, February 14, 2009, 8:30 AM Gabe wrote: --- On Mon, 2/9/09, Matthew Seaman m.sea...@infracaninophile.co.uk wrote: From: Matthew Seaman m.sea...@infracaninophile.co.uk Subject: Re: FreeBSD Preferred RAID controllers To: n...@att.net Cc: freebsd-questions@freebsd.org Date: Monday, February 9, 2009, 3:08 PM Gabe wrote: Now with a gstripe+gmirror setup, would it be possible to fail a specific drive on purpose? I mean fail a (good) drive, pull it out, replace it and rebuild(?) it. I know I know, but humor me. Yes. Cheers, Matthew Well, to 'fail' the drive, you'ld have to physically pull the drive from the chassis which will involve a power cycle unless you've got hot-swap drives. Of course, you should confirm that your system will boot with the RAID in a degraded state and that rebuilding the RAID will continue even if interrupted by a reboot. gmirror(8) passes those tests. You do have to type some commands to get a mirror to rebuild (examples are shown in the man page) unlike some hardware RAIDs where simply inserting an unused disk is sufficient. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW Hello again all, So I wanted to test out gmirror on software RAID so I installed a completely vanilla FBSD 7, as base an install as you can get, it hasn't even been on the network. Anyway, I did the following upon first boot to get gmirror going: # sysctl kern.geom.debugflags=17 Then: # gmirror label -vb round-robin gm0 /dev/ad0 Then: # gmirror load Then: # echo 'geom_mirror_load=YES' /boot/loader.conf Then I edited /etc/fstab to show: /dev/mirror/gm0s1bnoneswapsw 0 0 /dev/mirror/gm0s1a/ ufs rw 1 1 /dev/mirror/gm0s1e/tmpufs rw 0 0 /dev/mirror/gm0s1f/usrufs rw 2 2 /dev/mirror/gm0s1d/varufs rw 2 2 I then rebooted the system, once I setup the mirror: # gmirror insert gm0 /dev/ad1 # gmirror status and it shows as COMPLETE. Okay, here comes the annoying part, I've got hot-swappable bays and I went ahead and pulled the drive. I then tried to write to the disk so that it realizes the disk is no longer there: # touch file once I do that and execute: gmirror status it shows as degraded. All fine and dandy. However when it comes time to pop the drive back in the drive is not recognized at all. I mean, the green light on the bay comes on so it definitely makes a connection but then thats it, atacontrol list doesn't list it and gmirror status still shows the same, degraded. What gives? I wonder if this is hardware related? Bios related even? Any clues? See atacontrol(8) # atacontrol list shows what your system knows is there # atacontrol attach X where X is the channel number, probes and attaches any devices on that channel in exactly the same way it is done at system boot. See camcontrol(8) if you've got SCSI drives. Cheers, Matthew -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW They're SATA drives. The two drives are on the same channel when using atacontrol list. I'm unsure that atacontrol attach ata0 would work but I'll give it a shot, hopefully that works. I'll report back. Thanks again No go. atacontrol attach ata0 fails with Device exists probably because both sata drives are on the same channel. Still though, once inserted the kernel should show that it was inserted in /var/log/messages but it doesn't. ___ 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: FreeBSD Preferred RAID controllers
--- On Mon, 2/9/09, Matthew Seaman m.sea...@infracaninophile.co.uk wrote: From: Matthew Seaman m.sea...@infracaninophile.co.uk Subject: Re: FreeBSD Preferred RAID controllers To: n...@att.net Cc: freebsd-questions@freebsd.org Date: Monday, February 9, 2009, 3:08 PM Gabe wrote: Now with a gstripe+gmirror setup, would it be possible to fail a specific drive on purpose? I mean fail a (good) drive, pull it out, replace it and rebuild(?) it. I know I know, but humor me. Yes. Cheers, Matthew Well, to 'fail' the drive, you'ld have to physically pull the drive from the chassis which will involve a power cycle unless you've got hot-swap drives. Of course, you should confirm that your system will boot with the RAID in a degraded state and that rebuilding the RAID will continue even if interrupted by a reboot. gmirror(8) passes those tests. You do have to type some commands to get a mirror to rebuild (examples are shown in the man page) unlike some hardware RAIDs where simply inserting an unused disk is sufficient. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW Hello again all, So I wanted to test out gmirror on software RAID so I installed a completely vanilla FBSD 7, as base an install as you can get, it hasn't even been on the network. Anyway, I did the following upon first boot to get gmirror going: # sysctl kern.geom.debugflags=17 Then: # gmirror label -vb round-robin gm0 /dev/ad0 Then: # gmirror load Then: # echo 'geom_mirror_load=YES' /boot/loader.conf Then I edited /etc/fstab to show: /dev/mirror/gm0s1bnoneswapsw 0 0 /dev/mirror/gm0s1a/ ufs rw 1 1 /dev/mirror/gm0s1e/tmpufs rw 0 0 /dev/mirror/gm0s1f/usrufs rw 2 2 /dev/mirror/gm0s1d/varufs rw 2 2 I then rebooted the system, once I setup the mirror: # gmirror insert gm0 /dev/ad1 # gmirror status and it shows as COMPLETE. Okay, here comes the annoying part, I've got hot-swappable bays and I went ahead and pulled the drive. I then tried to write to the disk so that it realizes the disk is no longer there: # touch file once I do that and execute: gmirror status it shows as degraded. All fine and dandy. However when it comes time to pop the drive back in the drive is not recognized at all. I mean, the green light on the bay comes on so it definitely makes a connection but then thats it, atacontrol list doesn't list it and gmirror status still shows the same, degraded. What gives? I wonder if this is hardware related? Bios related even? Any clues? Thanks! ___ 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: FreeBSD Preferred RAID controllers
Gabe wrote: --- On Mon, 2/9/09, Matthew Seaman m.sea...@infracaninophile.co.uk wrote: From: Matthew Seaman m.sea...@infracaninophile.co.uk Subject: Re: FreeBSD Preferred RAID controllers To: n...@att.net Cc: freebsd-questions@freebsd.org Date: Monday, February 9, 2009, 3:08 PM Gabe wrote: Now with a gstripe+gmirror setup, would it be possible to fail a specific drive on purpose? I mean fail a (good) drive, pull it out, replace it and rebuild(?) it. I know I know, but humor me. Yes. Cheers, Matthew Well, to 'fail' the drive, you'ld have to physically pull the drive from the chassis which will involve a power cycle unless you've got hot-swap drives. Of course, you should confirm that your system will boot with the RAID in a degraded state and that rebuilding the RAID will continue even if interrupted by a reboot. gmirror(8) passes those tests. You do have to type some commands to get a mirror to rebuild (examples are shown in the man page) unlike some hardware RAIDs where simply inserting an unused disk is sufficient. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW Hello again all, So I wanted to test out gmirror on software RAID so I installed a completely vanilla FBSD 7, as base an install as you can get, it hasn't even been on the network. Anyway, I did the following upon first boot to get gmirror going: # sysctl kern.geom.debugflags=17 Then: # gmirror label -vb round-robin gm0 /dev/ad0 Then: # gmirror load Then: # echo 'geom_mirror_load=YES' /boot/loader.conf Then I edited /etc/fstab to show: /dev/mirror/gm0s1bnoneswapsw 0 0 /dev/mirror/gm0s1a/ ufs rw 1 1 /dev/mirror/gm0s1e/tmpufs rw 0 0 /dev/mirror/gm0s1f/usrufs rw 2 2 /dev/mirror/gm0s1d/varufs rw 2 2 I then rebooted the system, once I setup the mirror: # gmirror insert gm0 /dev/ad1 # gmirror status and it shows as COMPLETE. Okay, here comes the annoying part, I've got hot-swappable bays and I went ahead and pulled the drive. I then tried to write to the disk so that it realizes the disk is no longer there: # touch file once I do that and execute: gmirror status it shows as degraded. All fine and dandy. However when it comes time to pop the drive back in the drive is not recognized at all. I mean, the green light on the bay comes on so it definitely makes a connection but then thats it, atacontrol list doesn't list it and gmirror status still shows the same, degraded. What gives? I wonder if this is hardware related? Bios related even? Any clues? See atacontrol(8) # atacontrol list shows what your system knows is there # atacontrol attach X where X is the channel number, probes and attaches any devices on that channel in exactly the same way it is done at system boot. See camcontrol(8) if you've got SCSI drives. Cheers, Matthew -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW signature.asc Description: OpenPGP digital signature
Re: FreeBSD Preferred RAID controllers
--- On Sat, 2/14/09, Matthew Seaman m.sea...@infracaninophile.co.uk wrote: From: Matthew Seaman m.sea...@infracaninophile.co.uk Subject: Re: FreeBSD Preferred RAID controllers To: n...@att.net Cc: freebsd-questions@freebsd.org Date: Saturday, February 14, 2009, 8:30 AM Gabe wrote: --- On Mon, 2/9/09, Matthew Seaman m.sea...@infracaninophile.co.uk wrote: From: Matthew Seaman m.sea...@infracaninophile.co.uk Subject: Re: FreeBSD Preferred RAID controllers To: n...@att.net Cc: freebsd-questions@freebsd.org Date: Monday, February 9, 2009, 3:08 PM Gabe wrote: Now with a gstripe+gmirror setup, would it be possible to fail a specific drive on purpose? I mean fail a (good) drive, pull it out, replace it and rebuild(?) it. I know I know, but humor me. Yes. Cheers, Matthew Well, to 'fail' the drive, you'ld have to physically pull the drive from the chassis which will involve a power cycle unless you've got hot-swap drives. Of course, you should confirm that your system will boot with the RAID in a degraded state and that rebuilding the RAID will continue even if interrupted by a reboot. gmirror(8) passes those tests. You do have to type some commands to get a mirror to rebuild (examples are shown in the man page) unlike some hardware RAIDs where simply inserting an unused disk is sufficient. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW Hello again all, So I wanted to test out gmirror on software RAID so I installed a completely vanilla FBSD 7, as base an install as you can get, it hasn't even been on the network. Anyway, I did the following upon first boot to get gmirror going: # sysctl kern.geom.debugflags=17 Then: # gmirror label -vb round-robin gm0 /dev/ad0 Then: # gmirror load Then: # echo 'geom_mirror_load=YES' /boot/loader.conf Then I edited /etc/fstab to show: /dev/mirror/gm0s1bnoneswapsw 0 0 /dev/mirror/gm0s1a/ ufs rw 1 1 /dev/mirror/gm0s1e/tmpufs rw 0 0 /dev/mirror/gm0s1f/usrufs rw 2 2 /dev/mirror/gm0s1d/varufs rw 2 2 I then rebooted the system, once I setup the mirror: # gmirror insert gm0 /dev/ad1 # gmirror status and it shows as COMPLETE. Okay, here comes the annoying part, I've got hot-swappable bays and I went ahead and pulled the drive. I then tried to write to the disk so that it realizes the disk is no longer there: # touch file once I do that and execute: gmirror status it shows as degraded. All fine and dandy. However when it comes time to pop the drive back in the drive is not recognized at all. I mean, the green light on the bay comes on so it definitely makes a connection but then thats it, atacontrol list doesn't list it and gmirror status still shows the same, degraded. What gives? I wonder if this is hardware related? Bios related even? Any clues? See atacontrol(8) # atacontrol list shows what your system knows is there # atacontrol attach X where X is the channel number, probes and attaches any devices on that channel in exactly the same way it is done at system boot. See camcontrol(8) if you've got SCSI drives. Cheers, Matthew -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW They're SATA drives. The two drives are on the same channel when using atacontrol list. I'm unsure that atacontrol attach ata0 would work but I'll give it a shot, hopefully that works. I'll report back. Thanks again ___ 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: FreeBSD Preferred RAID controllers
--- On Sun, 2/8/09, Matthew Seaman m.sea...@infracaninophile.co.uk wrote: From: Matthew Seaman m.sea...@infracaninophile.co.uk Subject: Re: FreeBSD Preferred RAID controllers To: n...@att.net Cc: Wojciech Puchar woj...@wojtek.tensor.gdynia.pl, freebsd-questions@freebsd.org Date: Sunday, February 8, 2009, 11:55 AM Gabe wrote: --- On Sun, 2/8/09, Wojciech Puchar woj...@wojtek.tensor.gdynia.pl wrote: From: Wojciech Puchar woj...@wojtek.tensor.gdynia.pl I have to build a file server that will need to run a RAID 0+1 config If you want reliability, then use RAID10, not RAID0+1. For RAID10, you first create mirrored pairs of drives, then you stripe across all the mirrors. This is superior to RAID0+1 where you divide your drives into two equal pools, create a stripe across all the drives in each pool, and then mirror the stripes. Raw to usable space ratio is the same, performance characteristics are similar and good either way (some workloads, particularly those involving lots of small random IOs are particularly favourable on RAID10 (eg like the usage pattern of most RDBMses) whereas sequentially streaming large single files is happiest on RAID0+1 (eg. recording or playing video streams)). However imagine a RAID consisting of 2N drives. If one drive fails, then in RAID10, *one* of your N mirrors is degraded, and the rest work normally. In RAID0+1, it's one of the 2 *stripes* that is degraded -- effectively taking out half of your drives. Or to put it another way: given one drive has already died and the RAID is degraded, in either scenario, just one more disk death can take the RAID out completely. However with RAID10 there's exactly 1 drive whose death could have that effect -- failure of any of the other 2N-2 drives will degrade the RAID further, but it will still keep working. With RAID0+1 if the second disk to fail is any of the N drives from the other stripe, it will kill the whole RAID array. the best is gmirror+gstripe. of course for those who want to pay there are a lot of hardware solutions. Hey I'm all for saving money, but I'm unsure of the reliability of a 'software' solution vs a hardware one. Not to mention my biggest concern which is the failure of the Boot drive and how to recover from that using software raid. Software striping and mirroring is extremely reliable -- probably more so than using a hardware RAID card as there's simply less to go wrong. On the other hand hardware RAID offers some big performance advantages by being able to cache data in battery backed RAM[*] on the card, instead of requiring you to wait until it's been written to persistent storage on the drives themselves. While you can certaily boot from a gmirror RAID1, I don't believe it's possible to boot from a gstripe -- but because this all works via the geom framework, you can create stripes / mirrors at the filesystem level -- so you can have a small separate RAID1 to boot from and to hold the OS (either a dedicated pair of disks, or a pair of equal sized partitions, and then create a RAID10 over the rest of the disks to hold your data. I believe there is no requirement for the component parts of a gstripe to all be the same size Cheers, Matthew [*] For mirroring and striping, the only real justification for using hardware RAID is the performance benefit from the Battery Backup Unit on the RAID card. For RAID5 while a BBU is a *really good idea* it can justify itself by offloading parity calculations from the main CPU. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW Thank you, this is a very well-written response and I appreciate the time you took to type it all up. Now with a gstripe+gmirror setup, would it be possible to fail a specific drive on purpose? I mean fail a (good) drive, pull it out, replace it and rebuild(?) it. I know I know, but humor me. ___ 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: FreeBSD Preferred RAID controllers
Gabe wrote: Now with a gstripe+gmirror setup, would it be possible to fail a specific drive on purpose? I mean fail a (good) drive, pull it out, replace it and rebuild(?) it. I know I know, but humor me. Yes. Cheers, Matthew Well, to 'fail' the drive, you'ld have to physically pull the drive from the chassis which will involve a power cycle unless you've got hot-swap drives. Of course, you should confirm that your system will boot with the RAID in a degraded state and that rebuilding the RAID will continue even if interrupted by a reboot. gmirror(8) passes those tests. You do have to type some commands to get a mirror to rebuild (examples are shown in the man page) unlike some hardware RAIDs where simply inserting an unused disk is sufficient. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW signature.asc Description: OpenPGP digital signature
FreeBSD Preferred RAID controllers
Hello, I have to build a file server that will need to run a RAID 0+1 config and I'm looking for the best RAID controllers that run under Freebsd. My entire goal with using RAID 0+1 is having redundancy while utilizing most of the disk space. I realize the potential problems with this setup, the failure of the OS disk and booting for one and also dealing with the possibility of two drives failing within the same set. I guess I can deal with that(?) Anyway, What controllers have you found work well for you on F*BSD? ___ 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: FreeBSD Preferred RAID controllers
I have to build a file server that will need to run a RAID 0+1 config the best is gmirror+gstripe. of course for those who want to pay there are a lot of hardware solutions. ___ 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: FreeBSD Preferred RAID controllers
--- On Sun, 2/8/09, Wojciech Puchar woj...@wojtek.tensor.gdynia.pl wrote: From: Wojciech Puchar woj...@wojtek.tensor.gdynia.pl Subject: Re: FreeBSD Preferred RAID controllers To: Gabe n...@att.net Cc: freebsd-questions@freebsd.org Date: Sunday, February 8, 2009, 4:45 AM I have to build a file server that will need to run a RAID 0+1 config the best is gmirror+gstripe. of course for those who want to pay there are a lot of hardware solutions. ___ Hey I'm all for saving money, but I'm unsure of the reliability of a 'software' solution vs a hardware one. Not to mention my biggest concern which is the failure of the Boot drive and how to recover from that using software raid. Thanks ___ 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: FreeBSD Preferred RAID controllers
Gabe wrote: --- On Sun, 2/8/09, Wojciech Puchar woj...@wojtek.tensor.gdynia.pl wrote: From: Wojciech Puchar woj...@wojtek.tensor.gdynia.pl I have to build a file server that will need to run a RAID 0+1 config If you want reliability, then use RAID10, not RAID0+1. For RAID10, you first create mirrored pairs of drives, then you stripe across all the mirrors. This is superior to RAID0+1 where you divide your drives into two equal pools, create a stripe across all the drives in each pool, and then mirror the stripes. Raw to usable space ratio is the same, performance characteristics are similar and good either way (some workloads, particularly those involving lots of small random IOs are particularly favourable on RAID10 (eg like the usage pattern of most RDBMses) whereas sequentially streaming large single files is happiest on RAID0+1 (eg. recording or playing video streams)). However imagine a RAID consisting of 2N drives. If one drive fails, then in RAID10, *one* of your N mirrors is degraded, and the rest work normally. In RAID0+1, it's one of the 2 *stripes* that is degraded -- effectively taking out half of your drives. Or to put it another way: given one drive has already died and the RAID is degraded, in either scenario, just one more disk death can take the RAID out completely. However with RAID10 there's exactly 1 drive whose death could have that effect -- failure of any of the other 2N-2 drives will degrade the RAID further, but it will still keep working. With RAID0+1 if the second disk to fail is any of the N drives from the other stripe, it will kill the whole RAID array. the best is gmirror+gstripe. of course for those who want to pay there are a lot of hardware solutions. Hey I'm all for saving money, but I'm unsure of the reliability of a 'software' solution vs a hardware one. Not to mention my biggest concern which is the failure of the Boot drive and how to recover from that using software raid. Software striping and mirroring is extremely reliable -- probably more so than using a hardware RAID card as there's simply less to go wrong. On the other hand hardware RAID offers some big performance advantages by being able to cache data in battery backed RAM[*] on the card, instead of requiring you to wait until it's been written to persistent storage on the drives themselves. While you can certaily boot from a gmirror RAID1, I don't believe it's possible to boot from a gstripe -- but because this all works via the geom framework, you can create stripes / mirrors at the filesystem level -- so you can have a small separate RAID1 to boot from and to hold the OS (either a dedicated pair of disks, or a pair of equal sized partitions, and then create a RAID10 over the rest of the disks to hold your data. I believe there is no requirement for the component parts of a gstripe to all be the same size Cheers, Matthew [*] For mirroring and striping, the only real justification for using hardware RAID is the performance benefit from the Battery Backup Unit on the RAID card. For RAID5 while a BBU is a *really good idea* it can justify itself by offloading parity calculations from the main CPU. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW signature.asc Description: OpenPGP digital signature
