Performance in the mirrored system disk

[Sebastian Viudez Ortega]

Hi,

We have to install sortly a cluster composed of
two rp5470 and one VA7100 array. Each node
have two 18G internal disk and our idea is to
mirror one from the other with the MirrorDisk/UX.

The question is if that configuration can be
problematic, for example too much slow
because the mirrored disk is the system disk
and this is a software mirror.

Any experience in relation to?, any suggestion?

Regards.

S. Viudez.

[Michael Tully · Accepted solution]

Hi,

We use a number of 'A' and 'L'
class servers, all having mirrored
internal disks. You will find that
there will be a lot of read access
activity to these internal disks,
but not a lot of 'write' activity.
In fact this is quite a normal
occurance. In regards to performance
I cannot see too many problems as long
as most of the disk activity for your
applications and databases are
confined to your VA.

HTH
-Michael

[David Navarro]

Hi, Sebastian, when you install a cluster, normally you must mirror all disks. Normally you have protection in in you applications/data bases in a external array and OS in internal mirrored disks. I think, Mirrordisk/UX, decreases performance in a 3% aprox., But you should consider this lost of performance with the increased availability and security.

Suerte !

[David Navarro]

I forget to explain that in Mirrordosk/UX, you will loose performance in write access, but in read operations, OS uses both disks. That is, if you do more reads than writes, maybe your performace will be better.

[Marcin Wicinski]

Hi,
Thats fully supported configuration, dont bother performance - it's going to work well. Two internal disks shuold be on different SCSI controlers - each mirror will be supplied by deddicated controler (and data stream).
Later,

[Quin Hammes]

I agree. Mirroring like this is very standard and almost required for any critical system. The amount of writes to the system disks is typically so much lower than data disks that any performance loss due to having system disks mirrored will not even effect end users because their disk bottleneck will be the data disks and not the internal disks. The only time in which this might be a problem is if you are a doing alot of memory swapping but it still isn't enough of a problem not to mirror the disks.