EVA 8400 loops and speeds FOR ADVANCED

[Tsvetan]

Hi all,

I have to deside is it appropriate to configure FATA disks to separate loop and the 15kps disks to another 2 loops, or to mix all disk types in all the 3 loops?
Should the performance change or not?
I think that would be better to separete the slower disks to one loop, but...not sure
please advise

[Uwe Zessin]

A FATAl disk does not slow down loops - they always run at the same speed, but it can block valuable cache memory when it cannot write I/Os to media fast enough. One possible workaround is to disable write caching for the virtual disks on a FATAl disk group...
or avoid those disks completely.

[Tsvetan]

"cannot write I/Os to media fast enough" - doesn't this mean that the speed of the loop is afected by this?

[Uwe Zessin · Accepted solution]

No, a Fibre Channel Arbitrated Loop on the EVA-x400 transfers complete frames with 400 MegaBytes/second. The disk drives buffer complete frames after read from/before writing to the media, because this speed is slower.

[Tsvetan]

If I understand you correctly I should use the 3 loops with mixed disk type instead of separete FATA and FC loops?

[Uwe Zessin]

Yes, one should always equally distribute all disk drives from all disk groups (be it FC or FATAl) across all loops/enclosures.