Signed-off-by: Fabian Ebner <f.eb...@proxmox.com> --- local-zfs.adoc | 44 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+)
diff --git a/local-zfs.adoc b/local-zfs.adoc index b4fb7db..378cbee 100644 --- a/local-zfs.adoc +++ b/local-zfs.adoc @@ -431,3 +431,47 @@ See the `encryptionroot`, `encryption`, `keylocation`, `keyformat` and `keystatus` properties, the `zfs load-key`, `zfs unload-key` and `zfs change-key` commands and the `Encryption` section from `man zfs` for more details and advanced usage. + + +ZFS Special Device +~~~~~~~~~~~~~~~~~~ + +Since version 0.8.0 ZFS allows adding a `special` device to a pool, which is +then used to store metadata, deduplication tables and optionally small file +blocks. + +IMPORTANT: The redundancy of the `special` device should match the one of the +pool, since the `special` device is a point of failure for the whole pool. + +WARNING: Adding a `special` device to a pool cannot be undone! + +.Create a pool with `special` device and RAID-1: + + zpool create -f -o ashift=12 <pool> mirror <device1> <device2> special mirror <device3> <device4> + +.Add a `special` device to an existing pool with RAID-1: + + zpool add <pool> special mirror <device1> <device2> + +For ZFS datasets where the `special_small_blocks` property is set to a non-zero +value, the `special` device is used to store small file blocks up to that size. +Setting the `special_small_blocks` property on the pool will change the default +value of that property for all child ZFS datasets (for example all containers +in the pool will opt in for small file blocks). + +.Opt in for small file blocks pool-wide: + + zfs set special_small_blocks=<size> <pool> + +.Opt in for small file blocks for a single dataset: + + zfs set special_small_blocks=<size> <pool>/<filesystem> + +.Opt out from small file blocks for a single dataset: + + zfs set special_small_blocks=0 <pool>/<filesystem> + +Using a `special` device makes sense for pools with lots and lots of changing +metadata respectively small files. If you also have other, larger I/O on the +same pool then the benefit from using a `special` device might be even more +noticeable. It is recommended to use SSDs or NVMes for the `special` device. -- 2.20.1 _______________________________________________ pve-devel mailing list pve-devel@pve.proxmox.com https://pve.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
