Il 26/01/2011 18:58, Roberto Bifulco ha scritto:
[cut]
> from comparisons over the same harware we can be more confident that the
> results we get are still
> valid over a similar (clearly not exactly the same!!) configuration.
tipically tests are quite incomparable.
If you change disks (type, brand, size, number, raid level) or some
settings or hw you can obtain very different results.
IMHO the right way is to find how many IOPS do you need to archive your
load and then you can choose disk type, raid type, rpm etc
Tipically, the SAN type (iSCSI, FC, etc) doesn't affect IOPS ...so if
you need 4000 IOPS of a mixed 70/30 RW you can simply calculate the iron
you need to archive this.
Nevertheless, the connection type affects bandwidth between servers and
storage(s), latency and how many VMs you can put on a single piece of hw.
In other words, if you have good iron on the disk/controller side you
can archive for example 100 VMs but if the bottleneck is your connection
probably you have to reduce the overbooking level.
iSCSI tipically has a quite big overhead due to the protocol, FC, SAS,
native infiniband, AoE have very low overhead.
Best regards,
Christian
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