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Adicionar Como adicionar Special Dev a zpool

Daniel Sato
2025-10-09 16:35:15 -03:00
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ZFS Special Device
Since version 0.8.0 ZFS supports special devices. A special device in a pool is used to store metadata, deduplication tables, and optionally small file blocks.
A special device can improve the speed of a pool consisting of slow spinning hard disks with a lot of metadata changes. For example workloads that involve creating, updating or deleting a large number of files will benefit from the presence of a special device. ZFS datasets can also be configured to store whole small files on the special device which can further improve the performance. Use fast SSDs for the special device.
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>`
ZFS datasets expose the special_small_blocks=<size> property. size can be 0 to disable storing small file blocks on the special device or a power of two in the range between 512B to 1M. After setting the property new file blocks smaller than size will be allocated on the special device.
Important If the value for special_small_blocks is greater than or equal to the recordsize (default 128K) of the dataset, all data will be written to the special device, so be careful!
Setting the special_small_blocks property on a 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 all file smaller than 4K-blocks pool-wide:
`zfs set special_small_blocks=4K <pool>`
Opt in for small file blocks for a single dataset:
` zfs set special_small_blocks=4K <pool>/<filesystem>`
Opt out from small file blocks for a single dataset:
`zfs set special_small_blocks=0 <pool>/<filesystem>`