Nuno Silva wrote:Hi,What does this mean? The raid is syncing at 20MB/s, not each disk, so I do
Eyal Lebedinsky wrote:
I noticed that my 3-disk RAID was syncing at about 40MB/s, now that I3*40=120
added a fourth disk it goes at only 20+MB/s. This is on an idle machine.
4*20=80
not see what the multiplication is about.
Individually, each disk measures 60+MB/s with hdparm.And concurrent hdparms? Or some dd's concurrently?
I do not see this as relevant, but four concurrent hdparms (each to a
different disk) give about 30MB/s per disk. I expect the controller
to talk to the four disks at their full speed so concurrency should
not be the issue.
kernel: 2.6.13 on ia32
Controller: Promise SATAII150 TX4
Disks: WD 320GB SATA
Q: Is this the way the raid code works? The way the disk-io is
managed? Or
could it be due to the SATA controller?
You can isolate the performance drop with some dd's. Maybe this card is
in a pci32/33mhz and you're hitting the pci bus' limits? (120~130MB/sec).
'hdparm -T' gives about 1250 MB/sec so this is not the limiting
factor.