SAS disk performance drops a while after reboot.
- by Flamewires
So we have some workstations with identical hardware.
The Fedora14 box has a couple weeks uptime and still get good performance.
hdparm -tT /dev/sda
/dev/sda:
Timing cached reads: 21766 MB in 2.00 seconds = 10902.12 MB/sec
Timing buffered disk reads: 586 MB in 3.00 seconds = 195.20 MB/sec
The Cent 5.5 boxes however seem to be okay after a reboot,
/dev/sda:
Timing cached reads: 34636 MB in 2.00 seconds = 17354.64 MB/sec
Timing buffered disk reads: 498 MB in 3.01 seconds = 165.62 MB/sec
but some time later( unsure exactly, tested at approx 1 day uptime)
/dev/sda:
Timing cached reads: 2132 MB in 2.00 seconds = 1064.96 MB/sec
Timing buffered disk reads: 160 MB in 3.01 seconds = 53.16 MB/sec
drop to this. This is with very low load. I believe they all have the same bios settings. Any ideas what could cause this on Cent? Ask for more info. It might also be worth noting, that passing the --direct flag causes the slow boxes to perform similarly to the non-slow ones for buffered disk reads.
