ZFS regimen: scrub, scrub, scrub and scrub again.

[Artem Belevich]

On Wed, Jan 23, 2013 at 1:09 PM, Mark Felder <feld at feld.me> wrote:
> On Wed, 23 Jan 2013 14:26:43 -0600, Chris Rees <utisoft at gmail.com> wrote:
>
>>
>> So we have to take your word for it?
>> Provide a link if you're going to make assertions, or they're no more than
>> your own opinion.
>
>
> I've heard this same thing -- every vdev == 1 drive in performance. I've
> never seen any proof/papers on it though.

"1 drive in performance" only applies to number of random i/o
operations vdev can perform. You still get increased throughput. I.e.
5-drive RAIDZ will have 4x bandwidth of individual disks in vdev, but
would deliver only as many IOPS as the slowest drive as record would
have to be read back from N-1 or N-2 drived in vdev. It's the same for
RAID5. IMHO for identical record/block size RAID5 has no advantage
over RAID-Z for reads and does have disadvantage when it comes to
small writes. Never mind lack of data integrity checks and other bells
and whistles ZFS provides.

--Artem