On Fri, Mar 13, 2009 at 03:41:16AM +0100, Stefan de Konink wrote: > Mirroring will not increase performance because your RAID card will not > a priori know what files you are interested in, only the blocks you are > interested in and in the worst case will grab the same data from the > same disks and compare it ;)
In case of raid1 (mirroring) it should not compare data on simple read
but only do so in case of a reported ECC/disk block error.
Mirroring will increase performance with multiple concurrent readers
which is obviously the case with the OSM API Server. In the case of a
single reader you are right - it would not help latency but probably
streaming data (which would need intelligent read ahead)
So it is sensible to make it mirroring and it might even be a benefit to
do an 1 -> N mirroring.
Rule of thumb:
More concurrent readers -> More spindles
This is why 72GB disks are still common in storage systems.
Flo
--
Florian Lohoff f...@rfc822.org +49-171-2280134
Those who would give up a little freedom to get a little
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