Kevin Horton
Guru
- Joined
- Dec 2, 2015
- Messages
- 730
I'm pondering the pros and cons of adding a SLOG to my server. Looking at how I use the server, I don't expect many sync writes, so in
theory there should be no point to adding a SLOG. But looking at the output of zilstat, while I often see nothing but zeros, there are periods when I see writes to the ZIL.
The server serves several purposes:
There are no NFS shares, and no VMs. ZFS sync is set to "standard". There are two pools. The main pool serves the above purposes. The backup pool is a complete copy of the main pool, kept in sync with zfs replication. There is also a second server that has another complete copy, kept in sync with zfs replication from the main pool on the main server.
The problem is that I have no idea magnitude of ZIL activity is significant. I'd appreciate any comments from those who know how to interpret the output of zilstat. Note: although my workload shouldn't benefit from a SLOG, according to accepted wisdom, I have seen at least one report of a benefit when copying large numbers of small files, which is something that I do on occasion when using iTunes.app and Photos.app.
I'd appreciate any knowledgeable comment on the following zilstat output.
theory there should be no point to adding a SLOG. But looking at the output of zilstat, while I often see nothing but zeros, there are periods when I see writes to the ZIL.
The server serves several purposes:
- Document archiving, for documents that are not actively used. The documents are on SMB shares.
- Data storage for Apple iTunes and Photos libraries (very large numbers of small files).
- Plex server, with plex running in a jail, and the media stored on the server.
- Apple Time Machine backups from three computers, using AFP.
There are no NFS shares, and no VMs. ZFS sync is set to "standard". There are two pools. The main pool serves the above purposes. The backup pool is a complete copy of the main pool, kept in sync with zfs replication. There is also a second server that has another complete copy, kept in sync with zfs replication from the main pool on the main server.
The problem is that I have no idea magnitude of ZIL activity is significant. I'd appreciate any comments from those who know how to interpret the output of zilstat. Note: although my workload shouldn't benefit from a SLOG, according to accepted wisdom, I have seen at least one report of a benefit when copying large numbers of small files, which is something that I do on occasion when using iTunes.app and Photos.app.
I'd appreciate any knowledgeable comment on the following zilstat output.
Code:
zilstat -t 60 TIME N-Bytes N-Bytes/s N-Max-Rate B-Bytes B-Bytes/s B-Max-Rate ops <=4kB 4-32kB >=32kB 2018 Oct 3 20:46:50 24008128 400135 973624 105529344 1758822 4980736 1370 0 61 1309 2018 Oct 3 20:47:50 24481248 408020 1138984 120053760 2000896 4395008 1440 0 58 1382 2018 Oct 3 20:48:50 31471344 524522 1654392 126468096 2107801 5033984 1314 0 68 1246 2018 Oct 3 20:49:50 37227904 620465 2068936 137191424 2286523 6455296 1533 0 125 1408 2018 Oct 3 20:50:50 40671992 677866 1849368 154189824 2569830 6946816 1529 0 33 1496 2018 Oct 3 20:51:50 45287640 754794 1943512 176201728 2936695 7593984 1579 0 2 1577 2018 Oct 3 20:52:50 40446360 674106 1941648 163663872 2727731 5570560 1528 0 14 1514 2018 Oct 3 20:53:50 31088448 518140 1826176 110940160 1849002 5111808 1048 0 21 1027 2018 Oct 3 20:54:50 28072592 467876 1227072 110628864 1843814 4845568 1026 0 39 987 2018 Oct 3 20:55:50 23556800 392613 1366704 95031296 1583854 4112384 974 0 13 961