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OpenZFS on Linux and FreeBSD
https://openzfs.github.io/openzfs-docs
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zpool add should warn about adding a storage or special vdev to raidz #16460

Open tkittich opened 3 weeks ago

tkittich commented 3 weeks ago

Describe the feature would like to see added to OpenZFS

zpool add should warn about adding a storage or special vdev to a raidz pool that the added vdev cannot be removed later. zpool add should probably require -f or --allow-vdev-cant-be-removed flag in this case as well.

Also, the man page for zpool-remove is probably outdated. It states "Top-level vdevs can only be removed if the primary pool storage does not contain a top-level raidz vdev", which is not true because log and cache vdevs can be removed from a raidz pool.

How will this feature improve OpenZFS?

A warning about a storage or special vdev cannot be removed from a raidz pool would be very helpful and could prevent users from having to recreate the entire pool.

root@h00:/tmp/root# zpool add testpool special mirror /tmp/root/*.special
invalid vdev specification
use '-f' to override the following errors:
mismatched replication level: pool and new vdev with different redundancy, raidz and mirror vdevs, 2 vs. 1 (2-way)
>>**should be added**<< the storage or special vdev with raidz pool cannot be removed later

Additional context

There're many cases where users did not expect the vdevs couldn't be removed from raidz: #14312 , remove-or-migrate-special-vdev , why-doesnt-zfs-vdev-removal-work , remove_raidz_vdevs

amotin commented 3 weeks ago

Log and cache removal are a very different beasts. They do not use the device removal code, not moving any data, etc. Though may be possible to document in better indeed.

About warnings of special vdevs removal I am not sure I like it. Special vdev was designed to work in combination with RAIDZ and dRAID, so warning against its primary usage looks odd. Though, similar to above, may be it could be documented better.