mixing different spindles on same DAE

[newtoallthisstu]

Hello, i'm still stuck at the offers evaluation stage for a VI3 solution, but planning to buy by the end of september.

Some brands from which i got these offers will allow me to mix SATA2 7,2K RPM with FC2/4 10/15K RPM on the same disk enclosure, Dell and CX3-10C for example (or at least that's what i've been told by our dell rep.), but also FSC with FibreCAT SX80 and SAS together with SATA2 within the same DAE.

I agree the cost of an additional enclosure isn't that high, between 3-4.000€, but I'd prefer to invest that money into RAM, as the planned budget has already been defined.

Is it true that the "lowest" RPM spindle will bring the whole array performances to this lower value?

Of course, I couldn't find any mention of this issue in any manufacturer whitepaper. I've even been told that adding on the same controller more DAEs with different disk technologies would again bring everything down to the lowest performant spindle, because of the arbitrated loop.

Thanks for your suggestions, much appreciated as always.

[glynnd1]

The CX3-10 has only one redundant back end loop across all the DAEs.

Traffic in the loop can only run at one speed so if you mix 4Gbit FC with 2GBit FC they will be forced to run at 2Gbit FC.

Having said that, the SATA drives have 4Gbit FC interfaces, it is only the 10k RPM FC drives that have 2Gbit FC interfaces.

Hope this clears it up for you.

[newtoallthisstu]

Thanks glynnd1, that indeed cleared things up, I wasn't aware that SATA drives were boxed into FC4 trays.

Talking again about performances, the only drawback I will encounter, please correct me if I'm wrong, is that SP cache will take longer to write data on SATA arrays because of the 7.2K RPMs, the higher disk access timings and disks own cache (8MB vs 16MB), queuing faster writes directed to luns on native FC4 disk arrays until all slower writes to SATA2 are completed.

So the best solution would be to have two independent storage processors, one for fast expensive spindles, another one for cheaper/bigger/slower sata2 spindles, instead of a single loop between multiple DAEs..

Thanks!