zdb and zpool cache-files?

[Stilez]

Clean install 9.10.2-u1. I want to tune my setup and some of the commands for that are run via zdb, so I've set up a test server to see what impact various changes might make. I got this output:

$ zpool get all
NAME PROPERTY VALUE
Test_pool size 5.44T

$ zpool list Test_pool
NAME SIZE ALLOC FREE EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
Test_pool 5.44T 3.83T 1.60T - 51% 70% 1.00x ONLINE /mnt

$ zdb -S Test_pool
zdb: can't open 'Test_pool': No such file or directory

$zdb <pretty much any command> Test_pool
zdb: can't open 'Test_pool': No such file or directory

I can't get zdb to work at all. From googling, it looks like the issue is lack of a zfs or zpool cache file or some kind (See PCBSD redmine - appears to focus on FreeNAS 9.10 and this issue although on PCBSD Redmine; also on FreeNAS forum; see also same at ZFSonlinux), and solutions in those threads include using zdb -U zdb -U /data/zfs/zpool.cache (or some other path), or running zpool set cachefile=/boot/zfs/zpool.cache your_pool "if there is a need for a cachefile".

Can someone clarify whether the error I'm seeing is expected for FreeNAS, and, if I want to use zdb on 9.10.2-u1 (for its enhanced output information), how do I do so, or should I use something else?

If I need to create a "cache file", should I, what is it, and how much will adding one impact a live server?

 

[fracai]

Check the first two comments to this bug: https://bugs.pcbsd.org/issues/14536

I think what you want is: zdb -U /data/zfs/zpool.cache

 

[Mlovelace]

@fracai is correct. zdb by default (since freeNAS started using zfs for it's boot volume) points to the 'freenas-boot' volume. To use zdb on your pool(s) you need to point zdb to /data/zfs/zpool.cache

 

[Stilez]

Thanks for the replies, which helped. Also, request filed for this to be clearer if it's going to fail, since zdb is usually a go-to tool for advanced stats: https://bugs.pcbsd.org/issues/21373