Simulated DDT histogram: bucket allocated referenced Based on the results, you can decide if you can really save some space by deduping your data. Run the command on a low-IO period of time, because it reads the whole zpool. Zdb -S displays the predicted effect of deduplication, if enabled on the pool. If you're not sure that you should use deduplication or not, you can do a dry-run test of how duplicated your data really is. Zdb can be used to take an in-depth look at some other cool stuff too, like the current uberblock, see dedup statistics, inspect arc and zil stats, and so on.

Inspect dataset in-depth details (you can add more d’s for more verbosity): zdb -dd ĭisplay information about every spacemap record: zdb -MMM įor a much more detailed pool history than the output of zpool history -i command use: zdb -h If the pool is not imported or it lacks the zpool cache file. To check the vdev ashift used for the zpool, check the ZFS MOS configuration: zdb -C You can interact more effectively with ZFS using the zdb tool. Mixing disks with different blocksizes in the same pool can lead to caveats like performance leaks or inefficient space utilization. Either the value is set to '0' for auto blocksize recognition, or manually set to either ashift=12 for 4k blocksize disks or ashift=9 for 512b blocksize disks. A correlation between zfs 'blocksize' and the disk blocksize is the ashift parameter (which cannot be modified after the pool creation). When creating a pool, use disks with the same blocksize. Keep the used capacity under 80% for best performance. To make it persistent after a reboot, add the zfs_arc_max value to /etc/modprobe.d/zfs.conf file. To do so on-the-fly, increase the /sys/module/zfs/parameters/zfs_arc_max parameter value. ZFS is quite a memory hog, so allocate it more memory. If the ZFS filesystem is the backend for a storage system, then the performance of the filesystem can be increased by tuning its use of physical memory. Set the compression algorithm to lz4, default is lzjb. It can be used as a compromise between zfs atime=off and having it set to on.

This is simillar to ext4 atime (access time is only updated if the modified time or changed time changes). Logged access time is a property that can be as well turned off for improved pool performance. Try monitoring your system performance while using different types of checksumming algorithms and choose the proper one. The need for better system performance is understandable and you might think that the raid configuration and a backup are enough, so you'll disable checksumming. At that date the official page circulated some numbers like sha512 being 50% more performant than sha256, skein 80% and edon-R with more than 350% an increase in performance. Later implementations were made available sha512, skein and edon-R. It uses fletcher4 as the default algorithm for non-deduped data and sha256 for deduped data. ZFS is a highly reliable filesystem which uses checksumming to verify data and metadata integrity with on-the-fly repairs. When creating the pool, try not to combine disks of different speeds and sizes in the same VDEV, however, do try to mix the manufacturing date of the disks in order to prevent a data loss disaster. I’m going to cover some important aspects and share some useful information from my experience. ZFS is a complex and reliable filesystem so there are a lot of best practices and caveats when using it.

Zfs raid level openzfs