4 ms·

This is a home NAS with 50% free space, I rarely write stuff and don't even read much, yet it still managed to get super slow :( I don't use deduplication or co

This is a home NAS with 50% free space, I rarely write stuff and don't even read much, yet it still managed to get super slow :( I don't use deduplication or compression, and the good people over at #zfs have failed to find anything wrong multiple times. I think recreating the entire thing is about my only option at the moment.

magicalhippo 6y ago
That sucks, but also very weird. My pool, 2 vdevs each a 4-way RAID-Z1, has been used and abused for almost 7 years now. I've gone over the 85% mark but it still works fine, performance too. Some VM stuff but mostly media and similar. Do you mean slow IOPS or also sequential performance?
- StavrosK 6y ago
  It's mostly sequential performance, but it's also very odd. Deleting a single 2 GB file sometimes takes tens of seconds, or copying files from one volume to another will again be extremely slow.. .
  - magicalhippo 6y ago
    It does sound like fragmentation, which can still happen with a pool that's not filled under the "right" circumstances (usually related to workload vs configuration). But yeah sadly that's the one area where ZFS is less stellar. Once it's fragmented it's hard to fix. Easiest is to send/receive to another pool, but as you note that is not always feasible.
    - StavrosK 6y ago
      Is there no defragmentation tool? I do have lots of free space.
      - magicalhippo 6y ago
        Sadly no, not really. Part of it is that it's complicated due to copy-on-write and snapshots. Other part is manpower, it has not been a high-priority issue for most production pools it seems. Google for "block pointer rewrite". Assuming your free space fragmentation is not too bad (check output of zpool list, "frag" column is free space fragmentation level), you could just move files back and forth between the two. Assuming you don't have snapshots holding on to the files, this can help reduce the fragmentation. Otherwise you're stuck with the send/receive. Though I'd try the mailing list[1] to see if any of the gurus can help identify what's going wrong before attempting random ailments. [1]: https://zfsonlinux.topicbox.com/groups/zfs-discuss/ https://zfsonlinux.topicbox.com/groups/zfs-discuss/
        StavrosK 6y ago
        Hmm, I'll try the mailing list, thank you for your help!

magicalhippo 6y ago

That sucks, but also very weird. My pool, 2 vdevs each a 4-way RAID-Z1, has been used and abused for almost 7 years now. I've gone over the 85% mark but it still works fine, performance too. Some VM stuff but mostly media and similar. Do you mean slow IOPS or also sequential performance?

StavrosK 6y ago
It's mostly sequential performance, but it's also very odd. Deleting a single 2 GB file sometimes takes tens of seconds, or copying files from one volume to another will again be extremely slow.. .
- magicalhippo 6y ago
  It does sound like fragmentation, which can still happen with a pool that's not filled under the "right" circumstances (usually related to workload vs configuration). But yeah sadly that's the one area where ZFS is less stellar. Once it's fragmented it's hard to fix. Easiest is to send/receive to another pool, but as you note that is not always feasible.
  - StavrosK 6y ago
    Is there no defragmentation tool? I do have lots of free space.
    - magicalhippo 6y ago
      Sadly no, not really. Part of it is that it's complicated due to copy-on-write and snapshots. Other part is manpower, it has not been a high-priority issue for most production pools it seems. Google for "block pointer rewrite". Assuming your free space fragmentation is not too bad (check output of zpool list, "frag" column is free space fragmentation level), you could just move files back and forth between the two. Assuming you don't have snapshots holding on to the files, this can help reduce the fragmentation. Otherwise you're stuck with the send/receive. Though I'd try the mailing list[1] to see if any of the gurus can help identify what's going wrong before attempting random ailments. [1]: https://zfsonlinux.topicbox.com/groups/zfs-discuss/ https://zfsonlinux.topicbox.com/groups/zfs-discuss/
      - StavrosK 6y ago
        Hmm, I'll try the mailing list, thank you for your help!