2012-06-11 5:37, Edward Ned Harvey wrote:
From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
boun...@opensolaris.org] On Behalf Of Kalle Anka
Assume we have 100 disks in one zpool. Assume it takes 5 hours to scrub
disk. If I scrub the zpool, how long time will it take?
Will it scrub one disk at a time, so it will take 500 hours, i.e. in
serial? Or is it possible to run the scrub in parallel, so it takes 5h no
how many disks?
It will be approximately parallel, because it's actually scrubbing only the
used blocks, and the order it scrubs in will be approximately the order they
were written, which was intentionally parallel.
What the other posters said, plus: 100 disks is quite a lot
of contention on the bus(es), so even if it is all parallel,
the bus and CPU bottlenecks would raise the scrubbing time
somewhat above the single-disk scrub time.
Roughly, if all else is ideal (i.e. no/few random seeks and
a fast scrub at 100Mbps/disk), the SATA3 interface at 6Gbit/s
(on the order of ~600Mbyte/s) will be maxed out at about
6 disks. If your disks are colocated on one HBA receptacle
(i.e. via a backplane), this may be an issue for many disks
in an enclosure (a 4-lane link will sustain about 24 drives
at such speed, and that's not the market's max speed).
Further on, the PCI buses will become a bottleneck and the
CPU processing power might become one too, and for a box
with 100 disks this may be noticeable, depending on the other
architectural choices, components and their specs.
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