Messages in this thread |  | | Date | Thu, 20 Sep 2001 11:23:42 +0200 | From | David Hajek <> | Subject | Re: high cpu load with sw raid1 |
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Inlined.
On Thu, Sep 20, 2001, Jakob Řstergaard wrote: > On Thu, Sep 20, 2001 at 10:26:16AM +0200, David Hajek wrote: > > Hi, > > > > I have linux box with 70GB SW Raid1. This box runs for half > > a year without problems but now I meet the high cpu load > > problems. I suspect that it can be caused by not enough > > free disk space on this md device. I see following: > > > > 1 GB free - load > 5 > > 5 GB free - load < 1 > > RAID does not know about "free space" (that is a filesystem thing), so that > would be either some strange interaction between the filesystem and lower > layers, or a measurement error - I guess. > > High fragmentation could lead to extra filesystem activity, but that's not > really something the RAID can influence.
Why not? I do not say that it is cause be the RAID. It can be caused by filesystem. Do you think that fsck helps to defrag filesystem?
> > Please check that your disks are using DMA (hdparm /dev/hdX). You should > see something like: > > [root@eagle /root]# hdparm /dev/hda > > /dev/hda: > multcount = 16 (on) > I/O support = 0 (default 16-bit) > unmaskirq = 0 (off) > using_dma = 1 (on) <=========== INDICATES DMA > keepsettings = 0 (off) > nowerr = 0 (off) > readonly = 0 (off) > readahead = 8 (on) > geometry = 782/128/63, sectors = 6306048, start = 0 > > Without DMA you will see high CPU load from accessing the disks, regardless of > free space.
I use SCSI disks for this raid. Here is the output:
[root@marvin /root]# hdparm /dev/sda
/dev/sda: readonly = 0 (off) geometry = 8924/255/63, sectors = 143374738, start = 0 [root@marvin /root]# hdparm -t /dev/sda
/dev/sda: Timing buffered disk reads: 64 MB in 1.87 seconds = 34.22 MB/sec [root@marvin /root]#
I think disk speeds are ok - it works for really fine for half a year.
-- David Hajek hajek@idoox.com GSM: +420 604 352968 - You can't cheat the phone company.
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