Jesus Cea wrote:
Anton B. Rang wrote:
I have a two-vdev pool, just plain disk slices
If the vdev's are from the same disk, your are doomed.
ZFS tries to spread the load among the vdevs, so if the vdevs are from
the same disk, you will have a seek hell.
It is not clear to me that this is a problem. I used to believe that
it was always a problem. However, with modern drives using CTQ or
NCQ, it is not as bad as you would expect. Add drive caching to the
mix and it becomes very difficult to make a stand one way or the other.
Also, you should understand that the on-disk format for ZFS places
uberblocks at the beginning and end of the drive. Also, ditto
blocks are spread about using a diversity algorithm.
The best way to analyse such systems is to use statistical methods.
Predictions based upon simple seek models will no longer work.
Which leads me to... mirroring on one drive is better than not having
data protection. Ditto blocks for data will be better than mirroring
on one drive. Even when mirroring on one drive, the performance isn't
too bad for casual use.
-- richard
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