On Tue, Aug 12, 2008 at 1:40 PM, Henrik <henke@mac.se> wrote:
> Hi again all,
>
> Just wanted to give you an update.
>
> Talked to Dell tech support and they recommended using write-through(!)
> caching in RAID10 configuration. Well, it didn't work and got even worse
> performance.
Someone at Dell doesn't understand the difference between write back
and write through.
> Anyone have an estimated what a RAID10 on 4 15k SAS disks should generate in
> random writes?
Using sw RAID or a non-caching RAID controller, you should be able to
get close to 2xmax write based on rpms. On 7200 RPM drives that's
2*150 or ~300 small transactions per second. On 15k drives that's
about 2*250 or around 500 tps.
The bigger the data you're writing, the fewer you're gonna be able to
write each second of course.
> I'm really keen on trying Scotts suggestion on using the PERC/6 with mirror
> sets only and then make the stripe with Linux SW raid.
Definitely worth the try. Even full on sw RAID may be faster. It's
worth testing.
On our new servers at work, we have Areca controllers with 512M bbc
and they were about 10% faster mixing sw and hw raid, but honestly, it
wasn't worth the extra trouble of the hw/sw combo to go with.