mirroring primary swap space lvol2?

[John Guster]

A typical HP-UX system has lvol1 as /stand, lvol2 as primary swap space, lvol3 as /. One will add more RAM once device swapping kicks off to keep good performance. But before that happens, the device swap space serves as "reservation" to satisfy the requirement of launching a process, that is it is not really being used in terms of I/O. To save disk space, configure lvol2 as none mirrored while mirroring rest of lvols in vg00. Is it a good practice? will mirrored lvol2 as swap space helps performance?

[Steven E. Protter · Accepted solution]

Shalom,

No, mirring lvol2 will not help performance. It will make the system somewhat more reliable in the event of a disk failure, but many people advocate not mirroring swap because it can introduce problems.

I generally will mirror it for reliability concerns. Performance is not an issue in this decision.

SEP

[Pete Randall]

No swap, no system. Absolutely swap should be mirrored.


Pete

[A. Clay Stephenson]

If swap space is not being then them mirroring will have zero performance impact although mirroring in this context generally degrades performance but if you are swapping to any significant degree performance is so bad that the additional degradation due to the extra mirror write is insignificant. However, it is state-of-the-art stupid not to mirror every swap space for the simple reason that a disk failure will not crash the system nor will it require a shutdown to replace the failed disk. Even if the swap space is not being used, the system can and probably will crash when a swapspace becomes unavailable.

[Torsten.]

IMHO this is NOT a good practice.

If your disk with the swap on crash, your machine will crash too. If you try to boot from alternate, there is no swap space!
You will have 2 problems now.

Consider to mirror all LVOLs!

[John Guster]

It is crystal clear that no swap space no running system. One wants a H/A system, lvol2 swap space ought to be mirrored. Thanks for everyone's discussion.