Disk I/O Peformance

[John Jayaseelan]

Hi,

HP-UX 11.00 K370 server connected to the HASS array.

The HASS array contains no of 2GB and 4GB disks. Does the disk performance go down if the less capacity disks are replaced by 9GB * 18GB?

Thanks
John Jayaseelan

[Hein van den Heuvel]

Normally performance improves, unless you replace multiple smaller drivers by a single larger one.

The larger drives are more recent, and often spin and seek faster. At the very least they have the potential to transfer data faster as more bits fly by per rotation.

If you conceptually keep the same data on the new larger disk then is will occupy a much smaller band on the disk, dramatically improving seek time in the old data range.
100% full disk seek versus 20% range?

Go for it!
:-).

Hein.

[John Jayaseelan]

Hi,

Thanks for the reply.

What would be the performance if the data from 4 2GB 7200 rpm differential (HASS) disks are placed in 2 4GB 7200 rpm differential (HASS) disk?

Thanks
John Jayaseelan

[Hein van den Heuvel]

That's not a good Idea from a performance perspective.

More spindles is more speed... in general.

The defining factor here is concurreny of access.

If the usage of the drives is just a single stream reading a file at a time, then the 2*4GB drives will work a touch faster as the drive is likely to be able to deliver more (2x) mb/sec.

But if you have a typical multi-user, multi-application server, with concurrent, more or less independent usage over the drives, then 4 spindle with 4 seeks going on at the same time had more potential.

And then there are exception case where 4 spindles can work MUCH better. Two classic examples:
- a 'data' drive, and an 'index' drive, where an index access is followed by data acess and so on. Put them on a single spindle and two -near-local-on-their-own-drives activities become -max-seek-every-time-
- a 'log' drive and a 'data' drive, where the log drive is loaded and measured by MBSec and the data drive in IO/sec.

So... it all depends!

Cheers,

Hein.