Messages in this thread |  | | Date | Thu, 20 Sep 2001 11:10:48 +0200 | From | Jakob Østergaard <> | Subject | Re: high cpu load with sw raid1 |
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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.
> > I have to notice that this box is rather under heavy load > (1 GB cvs tree, nfs homes etc.) My question is whether this > load can depend on available disk space because I do not > see any suspect processes that can cause such a high load. > > Kernel: 2.2.19 > Patches: lfs + md + ide > RH6.2 + glibc-2.2.12
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.
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