Re: [zfs-discuss] Q : recommendations for zpool configuration
I went through this determination when setting up my pool. I decided to go with mirrors instead of raidz2 after considering the following: 1. Drive capacity in my box. At most, I can realistically cram 10 drives in my box and I am not interested in expanding outside of the box. I could go with 2.5 inch drives and fit a lot more, but I don't feel the necessity to do so. That being said, given the historic trend for mass storage drives to become cheaper over time, I have a feeling that I will be replacing drives to expand storage space long before the drives themselves start failing. The added redundancy of raidz2 is great, but I am betting that, barring a poorly manufactured drive, I will be replacing the drives with bigger drives before they have a chance to reach the end of their life. 2. Taking into account the above, it's a great deal easier on the pocket book to expand two drives at a time instead of four at a time. As bigger drives are always getting cheaper, I feel that I have a lot more flexibility with mirrors when it comes to expanding. If you have limitless physical space for drives, you might feel differently. 3. Mirrors are going to perform better than raidz. Again, redundancy is great, but so is performance. My setup is for home use. I want to keep my data safe but at the same time I am limited by cost and space. I think that given the tradeoff between the two, mirrors win. I feel that the chances of two drives in a mirror failing simultaneously are remote enough that I'll take the risk. 4. Again, I'm running this at home. It's not mission critical to me to have my data available 24/7. Redundancy is a convenience and not a necessity. Regardless of what you choose, backups are what will save your ass in the event of catastrophe. Having said that, I currently don't have a good backup solution and how to implement a good backup solution seems to be a hot topic on this list lately. Figuring out how to easily, effectively and cheaply back up multiple terabytes of storage is my number one priority at the moment. So anyways, all things considered, I prefer the better performance and easier expansion of storage space vs my physical space over a relatively small layer of extra redundancy. If you aren't doing anything that necessitates the added redundancy of raidz2, go with mirrors. Either way, if you care about your data, back it up. eric -- This message posted from opensolaris.org ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Q : recommendations for zpool configuration
On Sat, 20 Mar 2010, Eric Andersen wrote: 2. Taking into account the above, it's a great deal easier on the pocket book to expand two drives at a time instead of four at a time. As bigger drives are always getting cheaper, I feel that I have a lot more flexibility with mirrors when it comes to expanding. If you have limitless physical space for drives, you might feel differently. I agree with your arguments. Just make sure that you have a way to expand a mirror pair without losing redundancy. For example, make sure that there is a way to add a new device to act as the replacement without taking existing devices off line. Otherwise there is some possibility of data loss during the replacement. Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer,http://www.GraphicsMagick.org/ ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
[zfs-discuss] Q : recommendations for zpool configuration
Greetings I would like to get your recommendation how setup new pool. I have 4 new 1.5TB disks reserved to new zpool. I planned to crow/replace existing small 4 disks ( raidz ) setup with new bigger one. As new pool will be bigger and will have more personally important data to be stored long time, i like to ask your recommendations should i create recreate pool or just replace existing devices. I have noted there is now raidz2 and been thinking witch woul be better. A pool with 2 mirrors or one pool with 4 disks raidz2 So at least could some explain these new raidz configurations Thanks -- This message posted from opensolaris.org ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Q : recommendations for zpool configuration
A pool with a 4-wide raidz2 is a completely nonsensical idea. It has the same amount of accessible storage as two striped mirrors. And would be slower in terms of IOPS, and be harder to upgrade in the future (you'd need to keep adding four drives for every expansion with raidz2 - with mirrors you only need to add another two drives to the pool). Just my $0.02 On 19 March 2010 18:28, homerun petri.j.kunn...@gmail.com wrote: Greetings I would like to get your recommendation how setup new pool. I have 4 new 1.5TB disks reserved to new zpool. I planned to crow/replace existing small 4 disks ( raidz ) setup with new bigger one. As new pool will be bigger and will have more personally important data to be stored long time, i like to ask your recommendations should i create recreate pool or just replace existing devices. I have noted there is now raidz2 and been thinking witch woul be better. A pool with 2 mirrors or one pool with 4 disks raidz2 So at least could some explain these new raidz configurations Thanks -- This message posted from opensolaris.org ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Q : recommendations for zpool configuration
On Fri, Mar 19, 2010 at 2:34 PM, taemun tae...@gmail.com wrote: A pool with a 4-wide raidz2 is a completely nonsensical idea. It has the same amount of accessible storage as two striped mirrors. And would be slower in terms of IOPS, and be harder to upgrade in the future (you'd need to keep adding four drives for every expansion with raidz2 - with mirrors you only need to add another two drives to the pool). Just my $0.02 but it can survive on failure of 2 random disks in the pool. In striped mirror: mirror1 diskA diskB mirror2 diskC diskD In event diskA and diskB (or diskC and diskD) failed together, entire pool is lost. In raidz2: raidz2-1 diskA diskB diskC diskD Any combination of 2 disks can fail at same time and the pool will still intact. -- O ascii ribbon campaign - stop html mail - www.asciiribbon.org ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Q : recommendations for zpool configuration
On Fri, Mar 19, 2010 at 06:34:50PM +1100, taemun wrote: A pool with a 4-wide raidz2 is a completely nonsensical idea. No, it's not - not completely. It has the same amount of accessible storage as two striped mirrors. And would be slower in terms of IOPS, and be harder to upgrade in the future All that is true. If those things weren't as important to you as error recovery, raidz2 make fine sense: a 4-way raidz2 can tolerate the loss of any 2 disks. The mirror pool may die with the loss of the wrong 2 disks. Just my $0.02 Cost and benefit valuation are left to the user according to their circumstances. -- Dan. pgpl2dPbBOdFY.pgp Description: PGP signature ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Q : recommendations for zpool configuration
Thanks for comments So possible choises are : 1) 2 2-way mirros 2) 4 disks raidz2 BTW , can raidz have spare ? so is there one posible choise more : 3 disks raidz with 1 spare ? Here i prefer data availibility not performance. And if need sometime to expand / change setup it is then that time problem -- This message posted from opensolaris.org ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Q : recommendations for zpool configuration
On Fri, Mar 19, 2010 at 12:59:39AM -0700, homerun wrote: Thanks for comments So possible choises are : 1) 2 2-way mirros 2) 4 disks raidz2 BTW , can raidz have spare ? so is there one posible choise more : 3 disks raidz with 1 spare ? raidz2 is basically this, with a pre-silvered spare. With an unsilvered spare, you have no redundancy until the resilver completes, and if there are latent errors in the remaining non-redundant disks you may lose data. Other choices: - 4way raidz3 - 4way mirror Same space and fault tolerance, different performance. This is an easier choice, closer (but still not completely) to the nonsensical. Another choice again: - 2 separate pools, each a 2-disk mirror Data in one pool, backed up regularly by snapshot replication to the second. Same space as a 4-way mirror, but this has tolerance to some other kinds of problems that a single pool does not. Better still would be a backup pool in another machine/site. Perhaps the disks you are replacing can go to this purpose? -- Dan. pgpagv9YCTq4k.pgp Description: PGP signature ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Q : recommendations for zpool configuration
On Fri, March 19, 2010 02:28, homerun wrote: Greetings I would like to get your recommendation how setup new pool. I have 4 new 1.5TB disks reserved to new zpool. I planned to crow/replace existing small 4 disks ( raidz ) setup with new bigger one. As new pool will be bigger and will have more personally important data to be stored long time, i like to ask your recommendations should i create recreate pool or just replace existing devices. Replacing existing drives runs risks to the data -- you're deliberately reducing yourself to no redundancy for a while (while the resilver happens). It would probably be faster, and definitely safer, to back up the data, recreate the pool, and restore the data. I have noted there is now raidz2 and been thinking witch woul be better. A pool with 2 mirrors or one pool with 4 disks raidz2 A pool with 2 mirrors will have the same available space as a 4-disk raidz2. It will generally perform better. For small numbers of disks, I'm a big fan of using mirrors rather than RAIDZ. I've got an 8-disk hot-swap bay currently occupied by 3 2-disk pairs (with 2 slots for future expansion; maybe a hot spare, and a space to attach an additional disk during upgrades). When expanding a vdev by replacing devices, it can be done much more safely with a mirror than a RAIDZ group. With a mirror, you can attach a THIRD disk (in fact you can attach any number; one guy wrote about creating a 47-way mirror). So, instead of replacing one disk with a bigger one (eliminating your redundancy during the resilver), attach the bigger one as a third disk. When that resilver is done, you can attach the other new disk, if you have bay space; or detach one of the small disks and THEN attach the other new disk. When the second resilver is done, detach the last small disk, and you have now increased your mirror vdev size without ever reducing your redundancy below 2 copies. There's no equivalent process for a RAIDZ group. So at least could some explain these new raidz configurations RAIDZ is single parity -- one drive is redundant data. A RAIDZ vdev will withstand the failure of one drive without loss of data, but NOT the failure of 2 or more. A RAIDZ pool of N drives (all the same size) has N-1 drives worth of available capacity. RAIDZ2 is double parity -- two drives are given to redundant data. A RAIDZ2 vdev will withstand the failure of one or two drives without loss of data, but NOT the failure of 3 or more. A RAIDZ2 pool of N drives (all the same size) has N-2 drives worth of available capacity. A problem with modern large drives is that they take a long time to resilver in case of failure and replacement. During that period, if you started with one redundant drive, you're down to no redundant drives, meaning that a failure during the resilver could lose your data. (This is one of the many reasons you should have backups *in addition* to using redundant vdevs). This has driven people to develop higher levels of redundancy in parity schemes, such as RAIDZ2 (and RAIDZ3). -- David Dyer-Bennet, d...@dd-b.net; http://dd-b.net/ Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/ Photos: http://dd-b.net/photography/gallery/ Dragaera: http://dragaera.info ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
