Re: [Xen-users] xen disk io performance

[Jeff Sturm <jeff.sturm@xxxxxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Niels Dettenbach
> Sent: Tuesday, November 29, 2011 10:08 AM
> 
> > Solid-state storage helps, but you can often achieve the same effect
> > with lots of RAM, on the cheap.
> This is not correct in all cases as this still hardly depends from the model 
> (wear leveling
> etc.) and - not at least - the applications disk usage profile (i.e. hardly 
> parallel
> accesses etc.).

Yeah.  SSD isn't a cure-all, yet.

For what I need--high throughput on small random read requests--SSD looks like 
it may be a winner.  Haven't done a lot of testing yet, though.

> This means: a high quality and application specific optimized SAS RAID
> could be significantly "faster" then many SSDs.

Sure, it's possible.  Though it can be depressingly hard to find software that 
optimizes disk accesses well.  MySQL is particularly bad.  Oracle fares better.

> Another "ugly"
> point on SAN could be parallel access from other users / SAN clients to the 
> same
> physical disks or even swapping onto it from the same systems.

That's a big problem with virtualization too (bringing us back on topic).  Each 
host could do a good job at optimizing disk accesses.  But run them all at once 
off the same SAN and you could end up with a huge mess.

-Jeff



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