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zvol: Temporally disable blk-mq

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There was a report of zvol data loss (#15351) after enabling blk-mq on a
zvol backed with 16k physical block sized disks.  Out of an abundance of
caution, do not allow the user to enable blk-mq until we can look into
the issue.

Note that blk-mq was not enabled by default on zvols.  It was always
opt-in via the zvol_use_blk_mq module parameter.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Addresses: #15351
Closes #15378
This commit is contained in:
Tony Hutter
2023-10-10 08:57:48 -07:00
committed by Brian Behlendorf
parent 111ae3364c
commit a80e1f1c90
3 changed files with 1 additions and 70 deletions
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man/man4/zfs.4
-57
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@@ -2317,63 +2317,6 @@ If
.Sy zvol_threads
to the number of CPUs present or 32 (whichever is greater).
.
.It Sy zvol_blk_mq_threads Ns = Ns Sy 0 Pq uint
The number of threads per zvol to use for queuing IO requests.
This parameter will only appear if your kernel supports
.Li blk-mq
and is only read and assigned to a zvol at zvol load time.
If
.Sy 0
(the default) then internally set
.Sy zvol_blk_mq_threads
to the number of CPUs present.
.
.It Sy zvol_use_blk_mq Ns = Ns Sy 0 Ns | Ns 1 Pq uint
Set to
.Sy 1
to use the
.Li blk-mq
API for zvols.
Set to
.Sy 0
(the default) to use the legacy zvol APIs.
This setting can give better or worse zvol performance depending on
the workload.
This parameter will only appear if your kernel supports
.Li blk-mq
and is only read and assigned to a zvol at zvol load time.
.
.It Sy zvol_blk_mq_blocks_per_thread Ns = Ns Sy 8 Pq uint
If
.Sy zvol_use_blk_mq
is enabled, then process this number of
.Sy volblocksize Ns -sized blocks per zvol thread.
This tunable can be use to favor better performance for zvol reads (lower
values) or writes (higher values).
If set to
.Sy 0 ,
then the zvol layer will process the maximum number of blocks
per thread that it can.
This parameter will only appear if your kernel supports
.Li blk-mq
and is only applied at each zvol's load time.
.
.It Sy zvol_blk_mq_queue_depth Ns = Ns Sy 0 Pq uint
The queue_depth value for the zvol
.Li blk-mq
interface.
This parameter will only appear if your kernel supports
.Li blk-mq
and is only applied at each zvol's load time.
If
.Sy 0
(the default) then use the kernel's default queue depth.
Values are clamped to the kernel's
.Dv BLKDEV_MIN_RQ
and
.Dv BLKDEV_MAX_RQ Ns / Ns Dv BLKDEV_DEFAULT_RQ
limits.
.
.It Sy zvol_volmode Ns = Ns Sy 1 Pq uint
Defines zvol block devices behaviour when
.Sy volmode Ns = Ns Sy default :