ZFS on Linux: How to find the arc stats (was arcstat.py)

This has now changed; run the following to find the adaptive read cache stats (ARC):  
cat /proc/spl/kstat/zfs/arcstats
  You can gleam some really useful information out of how your RAM is being utilised and what your required ARC size might be from the results – this may be a topic for a future post, however!

ZFS on Linux: Zpool import failed

We upgraded a Proxmox box today which was running ZFS and ran into this rather scary looking error:  
zpool: ../../lib/libzfs/libzfs_import.c:356: Assertion `nvlist_lookup_uint64(zhp->zpool_config, ZPOOL_CONFIG_POOL_GUID, &theguid) == 0′ failed.
  Zpools would not import and zpool status did not work. Resolved (so far, anyhow, still testing) by running:  
apt-get install zfsutils
  Another good reason to have test environments…

ZFS on Linux (Ubuntu) – arcstat.py is now available! How do you run it?

UPDATE: This information is now out of date, see new post here.   One very handy ZFS-related command which has been missing from the standard ZFS on Linux implementation has been arcstat.py. This script provides a great deal of useful information about how effective your adaptive read cache (ARC) is.   ZFSoL 0.6.2 includes it, which you can now update to in Ubuntu with apt-get upgrade. But how do you actually use it when you upgrade? Easy. Assuming you have python installed, run the following (this works for 13.04 at least – we will check the others and update when we do):  
/usr/src/zfs-0.6.2/cmd/arcstat/arcstat.py
  This will provide you with the default readout, e.g. for our system which just rebooted:  
    time  read  miss  miss%  dmis  dm%  pmis  pm%  mmis  mm%  arcsz     c 21:33:13     3     1         33          1       33        0        0           1        33       2.5G   15G
  As you can see, since the system has just rebooted and hasn’t started caching requests the ARC size is quite small – 2.5G. This is an extremely useful tool to get an idea of how your ARC is performing – we will do a piece on interpreting the results soon!