Category: ZFS
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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,…
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ZFS: zpool replace returns error: cannot replace, devices have different sector alignment
Trying to replace a failed SSD in a zpool we encountered the following error: cannot replace 4233944908106055 with ata-INTEL_SSDSC2BW240A4_CVD02KY2403GN: devices have different sector alignment The pool was aligned to 4k sectors – e.g. ashift=12 – whereas the new SSD was aligned to 512b sectors. There’s a quick and easy fix to this –…
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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…
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ZFS: Adding a new mirror to an existing ZFS pool
Mirrored vdevs are great for performance and it is quite straight-forward to add a mirrored vdev to an existing pool (presumably one with one or more similar vdevs already): zpool add [poolname] mirror [device01] [device02] [device03] If it’s a two-way mirror you will only have two devices in the above. An example…
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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UPDATE: This information is now out of date, see new post here.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,…
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ZFS: Renaming a zpool
If you’ve imported a pool from another system and want to change the name or have just changed your mind, this is actually quite straightforward to do. Run the following (as root): zpool export [poolname] As an example, for a pool named tank which we wish to rename notankshere: zpool export tank Then run:…
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Western Digital Green drive resilver rates
We get asked fairly regularly about resilver rates for ZFS pools – these matter as it impacts on how quickly a vdev with faulty disks can rebuild data onto a fresh disk, as well as how quickly you can swap one disk for another. The longer it takes to rebuild the vdev after…
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ZFS on Ubuntu error: Failed to load ZFS module stack
If you see the above error in a fresh installation of ZFS on Ubuntu one cause may be that the package build-essentials wasn’t installed prior to installing the ubuntu-zfs package; run: sudo apt-get purge ubuntu-zfs then check for the remaining packages with the following: dpkg –list | grep zfs …and…
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ZFS: How to change the compression level
By default ZFS uses the lzjb compression algorithm; you can select others when setting compression on a ZFS folder. To try another one do the following: sudo zfs set compression=gzip [zfs dataset] This changes the compression algorithm to gzip. By default this sets it to gzip-6 compression; we can actually specify what level…
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ZFS: Replacing a drive with a larger drive within a vdev
One way to expand the capacity of a zpool is to replace each disk with a larger disk; once the last disk is replaced the pool can be expanded (or will auto-expand, depending on your pool settings). To do this we do the following: zpool replace [poolname] [old drive] [new drive] e.g.: …