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I certainly wanted this. I even heckled Bill Moore about it. Having gone through the expansion the old way (replace each drive one at a time with a larger one),
by FullyFunctional 5y ago
I certainly wanted this. I even heckled Bill Moore about it. Having gone through the expansion the old way (replace each drive one at a time with a larger one), this looks a lot simpler. Unfortunately it appears to not work with simple mirror and stripes (~ RAID10) so it will make no difference for me. (Drives are cheap but performance is not -> RAID10).
- arwineap 5y agoThis looks different than the old way The old way ( as you referenced ) was to replace each disk one by one with a larger one. If I'm understanding this right, and please correct me, this feature will allow you to add a 5th disk to a 4 disk raidz And if I'm right about that, then this feature wouldn't really make sense for RAID10 anyway
- FullyFunctional 5y agoI love ZFS but this is something that just works in btrfs; mirror just means all blocks live in two physical locations. You certainly can do that even with an odd number of drives. However ZFS is more rigid and doesn’t allow flowing blocks like this, nor dynamic defragmentation.
- deagle50 5y agoWould you use raid 5/6 in btrfs?
- NavinF 5y agoThe btrfs raid5/6 write hole is still around, if anyone’s wondering. Though it was only recently that btrfs started warning users that it would eat their data: https://www.phoronix.com/scan.php?page=news_item&px=Btrfs-Warning-RAID5-RAID6 https://www.phoronix.com/scan.php?page=news_item&px=Btrfs-Wa...
- mrlonglong 5y agoI'll certainly attest to that, btrfs did that to me. Moved over to ZFS and all that went away.
- NavinF 5y agoWhat are you on about? The submission is about raidz. Adding drives to a mirror has worked in zfs since prehistoric times. “zpool attach test_pool sda sdc” will mirror sda to sdc. If sda was already mirrored with sdb, you now have a triple-mirror with sda, sdb, and sdc.
- wtallis 5y ago> If sda was already mirrored with sdb, you now have a triple-mirror with sda, sdb, and sdc. You probably already know this, but btrfs offers a different option. Its "RAID1" mode would not result in the three drives storing your data in triplicate but rather still stores data in duplicate but with a usable capacity that's 1.5x that of a single driver's capacity. To get the ZFS behavior you describe, btrfs offers a "RAID1c3" mode, but that's a much less interesting feature.
- NavinF 5y agoHuh I didn’t know that. Seems like a niche feature, but it’s still pretty neat!
- rodgerd 5y agoIt's a neat feature for SOHO-type users, and takes advantage of the fact that the RAID layer knows about the FS. The first implementation that I know of is Drobo's filesystem. Asymmetric RAID is probably the only config that I'd like to see in ZFS - being able to have (say) an 8TB drive and two 4TB drives, and have 8TB of mirrored space is quite nice when you're just buying commodity kit and don't want to have to retire/match drives all the time when growing mirrors.
- wtallis 5y agoYep, SOHO use cases are where this kind of capability is really useful. ZFS is great when you buy drives by the dozen, but even with this feature it's still inconveniently inflexible if you only have the budget to be upgrading or expanding one drive at a time.
- chasil 5y agoLike Btrfs, ZFS stores multiple copies of metatdata blocks when possible. Forcing ZFS to store multiple data blocks also can be done. This is great for ZFS on flash drives. https://docs.oracle.com/cd/E19253-01/819-5461/gevpg/index.html https://docs.oracle.com/cd/E19253-01/819-5461/gevpg/index.ht...
- FullyFunctional 5y agoThat not the same thing. Bill Tallis below explained it better than I did though.
- chungy 5y agoSimple mirrors and stripes could always be expanded (and reduced, too). RAID-Z has been special.
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