5 ms·

> But nested mirrors still suffer from the same issue of losing a drive and you lose everything. Are you referring to mirroring a volume or dataset on a single

> But nested mirrors still suffer from the same issue of losing a drive and you lose everything. Are you referring to mirroring a volume or dataset on a single disk? Why would you want to do that instead of mirroring among multiple drives?

gigatexal 9y ago
how would you set up a large pool? two sets of say 5 disks in a mirror raidz1 would still fail if a disk in one set failed and a disk in the other set failed. I guess you could do a stripe setup of 5 sets of 2 disks in mirrors. Still it seems wicked risky to me. I do agree though mirroring has been the best for speed but a lot of that changes with nicer SSDs especially NVMe ones.
- aeorgnoieang 9y ago
  I was curious about what a "nested" mirror is really. What exactly is nested? I'd setup a large pool with mirror vdevs, i.e. n sets of 2 disks per mirror. My half-remembered reasoning was that backups manage the risk you'll lose data. But replacing a disk in a mirror vdev is much easier, and faster, than doing so with RAIDZ. The risk of RAIDZ is that resilvering impacts multiple vdevs, is much more intensive than a simple mirror resilvering, and thus the probability that additional drives will fail is much higher. Here's a blog post that I definitely read the last time I was reading up on this: - [ZFS: You should use mirror vdevs, not RAIDZ. – JRS Systems: the blog](http://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/ http://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs-...)
- aeorgnoieang 9y ago
  A Reddit post about that blog post in my other reply: - [You should use mirror vdevs, not RAIDZ. : DataHoarder](https://www.reddit.com/r/DataHoarder/comments/2v0quc/you_should_use_mirror_vdevs_not_raidz/?st=j5vfwpao&sh=926670a0 https://www.reddit.com/r/DataHoarder/comments/2v0quc/you_sho...)
  - gigatexal 9y ago
    I wonder if resilvering is still an issue with SSDs. But I cede your point, nested vdevs of two disks making mirrors makes sense. It doesn't sit well still, but makes sense
  - gigatexal 9y ago
    According to OpenZFS's changelog for v 0.7 resilvering is smarter now: https://github.com/zfsonlinux/zfs/releases/tag/zfs-0.7.0 https://github.com/zfsonlinux/zfs/releases/tag/zfs-0.7.0

gigatexal 9y ago

how would you set up a large pool? two sets of say 5 disks in a mirror raidz1 would still fail if a disk in one set failed and a disk in the other set failed. I guess you could do a stripe setup of 5 sets of 2 disks in mirrors. Still it seems wicked risky to me. I do agree though mirroring has been the best for speed but a lot of that changes with nicer SSDs especially NVMe ones.

aeorgnoieang 9y ago
I was curious about what a "nested" mirror is really. What exactly is nested? I'd setup a large pool with mirror vdevs, i.e. n sets of 2 disks per mirror. My half-remembered reasoning was that backups manage the risk you'll lose data. But replacing a disk in a mirror vdev is much easier, and faster, than doing so with RAIDZ. The risk of RAIDZ is that resilvering impacts multiple vdevs, is much more intensive than a simple mirror resilvering, and thus the probability that additional drives will fail is much higher. Here's a blog post that I definitely read the last time I was reading up on this: - [ZFS: You should use mirror vdevs, not RAIDZ. – JRS Systems: the blog](http://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/ http://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs-...)
aeorgnoieang 9y ago
A Reddit post about that blog post in my other reply: - [You should use mirror vdevs, not RAIDZ. : DataHoarder](https://www.reddit.com/r/DataHoarder/comments/2v0quc/you_should_use_mirror_vdevs_not_raidz/?st=j5vfwpao&sh=926670a0 https://www.reddit.com/r/DataHoarder/comments/2v0quc/you_sho...)
- gigatexal 9y ago
  I wonder if resilvering is still an issue with SSDs. But I cede your point, nested vdevs of two disks making mirrors makes sense. It doesn't sit well still, but makes sense
- gigatexal 9y ago
  According to OpenZFS's changelog for v 0.7 resilvering is smarter now: https://github.com/zfsonlinux/zfs/releases/tag/zfs-0.7.0 https://github.com/zfsonlinux/zfs/releases/tag/zfs-0.7.0