mirrored root drives not equally busy?

[James Sohr_2]

Can anyone explain to me why a boot drive and its mirror would not be equally busy? They obviously contain the same data... so what would cause one drive to get used more than another?

Thanks,
James

sar -d output:
device %busy avque r+w/s blks/s avwait avserv
Average c1t6d0 28.78 2.72 39 475 18.58 21.33
Average c2t6d0 19.24 2.99 30 433 18.57 19.48

[Mark Greene_1]

It's only mirroring the writes, not the reads. I think.

mark

[Michael Tully]

I'll second the vote. I did the same test on a coupld of my systems and get the same results.

Seeing the primary say it is disk1 is the booted drive then the reads would be from this. The mirroring makes sure that both disks are updated with the writes. The only way to even this up would be to add further disks and do LVM striping.

[A. Clay Stephenson]

1) It's just possible that you are not fully mirrored so check each LVOL to be sure and don't overlook primary swap.

2) Writes should always go to both drives but reads are assigned to the drive with the shortest i/o queue at the moment. That's where the performance benefits of mirroring come into play.