On Wed, Jan 26, 2011 at 07:15:41PM +0100, Christian Zoffoli wrote:
> 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.
>
Not true today.
TCP/IP is hardware offloaded nowadays, and many NICs also
have hardware iSCSI offloading.
Also AoE is not really faster than iSCSI, since TCP/IP
is hardware offloaded these days.. iSCSI is more flexible
and more widely supported than AoE.
-- Pasi
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