Hi Phil, long time, no see. comments embedded below

On Tue, Dec 6, 2022 at 3:35 AM Phil Harman <phil.har...@gmail.com> wrote:

> I have a number of "ZFS backup" servers (about 1PB split between four
> machines).
>
> Some of them have 16x 18TB drives, but a couple have a mix of 12TB and
> 14TB drives (because that's what we had).
>
> All are running Ubuntu 20.04 LTS (with a snapshot build) or 22.04 LTS
> (bundled).
>
> We're just doing our first replace (actually swapping in a 16TB drive for
> a 12TB because that's all we have).
>
> root@hqs1:~# zpool version
> zfs-2.1.99-784_gae07fc139
> zfs-kmod-2.1.99-784_gae07fc139
> root@hqs1:~# zpool status
>   pool: hqs1p1
>  state: DEGRADED
> status: One or more devices is currently being resilvered.  The pool will
> continue to function, possibly in a degraded state.
> action: Wait for the resilver to complete.
>   scan: resilver in progress since Mon Dec  5 15:19:31 2022
> 177T scanned at 2.49G/s, 175T issued at 2.46G/s, 177T total
> 7.95T resilvered, 98.97% done, 00:12:39 to go
> config:
>
> NAME                                      STATE     READ WRITE CKSUM
> hqs1p1                                    DEGRADED     0     0     0
>  draid2:3d:16c:1s-0                      DEGRADED     0     0     0
>    780530e1-d2e4-0040-aa8b-8c7bed75a14a  ONLINE       0     0     0
>  (resilvering)
>    9c4428e8-d16f-3849-97d9-22fc441750dc  ONLINE       0     0     0
>  (resilvering)
>    0e148b1d-69a3-3345-9478-343ecf6b855d  ONLINE       0     0     0
>  (resilvering)
>    98208ffe-4b31-564f-832d-5744c809f163  ONLINE       0     0     0
>  (resilvering)
>    3ac46b0a-9c46-e14f-8137-69227f3a890a  ONLINE       0     0     0
>  (resilvering)
>    44e8f62f-5d49-c345-9c89-ac82926d42b7  ONLINE       0     0     0
>  (resilvering)
>    968dbacd-1d85-0b40-a1fc-977a09ac5aaa  ONLINE       0     0     0
>  (resilvering)
>    e7ca2666-1067-f54c-b723-b464fb0a5fa3  ONLINE       0     0     0
>  (resilvering)
>    318ff075-8860-e84e-8063-f77775f57a2d  ONLINE       0     0     0
>  (resilvering)
>    replacing-9                           DEGRADED     0     0     0
>      2888151727045752617                 UNAVAIL      0     0     0  was
> /dev/disk/by-partuuid/85fa9347-8359-4942-a20d-da1f6016ea48
>      sdd                                 ONLINE       0     0     0
>  (resilvering)
>    fd69f284-d05d-f145-9bdb-0da8a72bf311  ONLINE       0     0     0
>  (resilvering)
>    f40f997a-33a1-2a4e-bb8d-64223c441f0f  ONLINE       0     0     0
>  (resilvering)
>    dbc35ea9-95d1-bd40-b79e-90d8a37079a6  ONLINE       0     0     0
>  (resilvering)
>    ac62bf3e-517e-a444-ae4f-a784b81cd14c  ONLINE       0     0     0
>  (resilvering)
>    d211031c-54d4-2443-853c-7e5c075b28ab  ONLINE       0     0     0
>  (resilvering)
>    06ba16e5-05cf-9b45-a267-510bfe98ceb1  ONLINE       0     0     0
>  (resilvering)
>  draid2:3d:6c:1s-1                       ONLINE       0     0     0
>    be297802-095c-7d43-9132-360627ba8ceb  ONLINE       0     0     0
>    e849981c-7316-cb47-b926-61d444790518  ONLINE       0     0     0
>    bbc6d66d-38e1-c448-9d00-10ba7adcd371  ONLINE       0     0     0
>    9fb44c95-5ea6-2347-ae97-38de283f45bf  ONLINE       0     0     0
>    b212cae5-5068-8740-b120-0618ad459c1f  ONLINE       0     0     0
>    8c771f6b-7d48-e744-9e25-847230fd2fdd  ONLINE       0     0     0
> spares
>  draid2-0-0                              AVAIL
>  draid2-1-0                              AVAIL
>
> errors: No known data errors
> root@hqs1:~#
>
> Here's a snippet of zpool iostat -v 1 ...
>
>                                             capacity     operations
> bandwidth
> pool                                      alloc   free   read  write
> read  write
> ----------------------------------------  -----  -----  -----  -----
>  -----  -----
> hqs1p1                                     178T  67.1T  5.68K    259
> 585M   144M
>   draid2:3d:16c:1s-0                       128T  63.1T  5.66K    259
> 585M   144M
>     780530e1-d2e4-0040-aa8b-8c7bed75a14a      -      -    208      0
>  25.4M      0
>     9c4428e8-d16f-3849-97d9-22fc441750dc      -      -   1010      2
> 102M  23.7K
>     0e148b1d-69a3-3345-9478-343ecf6b855d      -      -    145      0
>  34.1M  15.8K
>     98208ffe-4b31-564f-832d-5744c809f163      -      -    101      1
>  28.3M  7.90K
>     3ac46b0a-9c46-e14f-8137-69227f3a890a      -      -    511      0
>  53.5M      0
>     44e8f62f-5d49-c345-9c89-ac82926d42b7      -      -     12      0
>  4.82M      0
>     968dbacd-1d85-0b40-a1fc-977a09ac5aaa      -      -     22      0
>  5.43M  15.8K
>     e7ca2666-1067-f54c-b723-b464fb0a5fa3      -      -    227      2
>  36.7M  23.7K
>     318ff075-8860-e84e-8063-f77775f57a2d      -      -    999      1
>  83.1M  7.90K
>     replacing-9                               -      -      0    243
>  0   144M
>       2888151727045752617                     -      -      0      0
>  0      0
>       sdd                                     -      -      0    243
>  0   144M
>     fd69f284-d05d-f145-9bdb-0da8a72bf311      -      -    306      0
>  54.5M  15.8K
>     f40f997a-33a1-2a4e-bb8d-64223c441f0f      -      -     47      0
>  16.9M      0
>     dbc35ea9-95d1-bd40-b79e-90d8a37079a6      -      -    234      0
>  16.7M  15.8K
>     ac62bf3e-517e-a444-ae4f-a784b81cd14c      -      -    417      0
>  15.9M      0
>     d211031c-54d4-2443-853c-7e5c075b28ab      -      -    911      0
>  48.4M  15.8K
>     06ba16e5-05cf-9b45-a267-510bfe98ceb1      -      -    643      0
>  60.1M  15.8K
>   draid2:3d:6c:1s-1                       50.6T  3.96T     19      0
> 198K      0
>     be297802-095c-7d43-9132-360627ba8ceb      -      -      3      0
>  39.5K      0
>     e849981c-7316-cb47-b926-61d444790518      -      -      2      0
>  23.7K      0
>     bbc6d66d-38e1-c448-9d00-10ba7adcd371      -      -      2      0
>  23.7K      0
>     9fb44c95-5ea6-2347-ae97-38de283f45bf      -      -      3      0
>  39.5K      0
>     b212cae5-5068-8740-b120-0618ad459c1f      -      -      3      0
>  39.5K      0
>     8c771f6b-7d48-e744-9e25-847230fd2fdd      -      -      1      0
>  31.6K      0
> ----------------------------------------  -----  -----  -----  -----
>  -----  -----
>
> Lots of DRAID goodness there. Seems to be resilvering a q good whack.
>
> My main question is: why have the DRAID vdevs been so disproportionately
> allocated?
>

When doing a replace to disk, which is not the same as replace to logical
spare, then the
disk's write performance is the bottleneck. The draid rebuild time
improvements only apply
when rebuilding onto a logical spare.

The data should be spread about nicely, but I don't think you'll see that
with a short time interval.
Over perhaps 100 seconds or so, it should look more randomly spread.
 -- richard



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