[CFR][ZFS] merge Illumos rev. 13379 (writing to imbalanced vdevs)

[Pawel Jakub Dawidek]

On Mon, Jun 20, 2011 at 11:16:50AM +0200, Martin Matuska wrote:
> zfs tries to allocate blocks evenly across all devices. This means when
> devices are imbalanced zfs will lots of CPU searching for space on devices
> which tend to be pretty full.
> 
> https://www.illumos.org/issues/1051
> https://www.illumos.org/projects/illumos-gate/repository/revisions/13379
> 
> If there are no objections, I will commit this to -HEAD

Some comments inline.

> @@ -5137,6 +5138,7 @@
>  	 */
>  	kernel_init(FREAD | FWRITE);
>  	VERIFY(spa_open(zs->zs_pool, &spa, FTAG) == 0);
> +	spa->spa_debug = B_TRUE;
>  	zs->zs_spa = spa;
>  
>  	spa->spa_dedup_ditto = 2 * ZIO_DEDUPDITTO_MIN;

Do we want spa debug to be enabled by default? If we don't then please
enable it only when DEBUG is defined.

>  /*
> + * This value defines the number of allowed allocation failures per vdev.
> + * If a device reaches this threshold in a given txg then we consider skipping
> + * allocations on that device.
> + */
> +int zfs_mg_alloc_failures;

In FreeBSD we probably want sysctl and loader tunable for this.
I think it should be fine to make sysctl read/write, but I haven't
looked very closely.

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
FreeBSD committer                         http://www.FreeBSD.org
Am I Evil? Yes, I Am!                     http://yomoli.com
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