[linux-lvm] LVM and *bad* performance (no striping)
Urs Thuermann
urs at isnogud.escape.de
Sun May 27 09:47:30 UTC 2001
Andreas Dilger <adilger at turbolinux.com> writes:
> /dev/vgtest/lvtest = real 66.909s user 0.440s sys 10.420 *** 5x as slow
> /dev/vgtest/lvtest = real 70.135s user 0.520s sys 11.390 *** 5x as slow
>
> /dev/vgtest3/lvtest = real 63.552s user 0.510s sys 10.290s *** 6x as slow
> /dev/vgtest3/lvtest = real 62.354s user 0.610s sys 10.020s *** 6x as slow
This is similar to the worst case numbers I have measured.
> I'm not sure if it is an SMP or SCSI issue, or what. Urs, do you also
> have an SMP system? Maybe there are locking slowdowns under SMP and
> not under UP?
No. It's a single Pentium II, 333MHz, kernel 2.4.3 with lvm-0.9.1_beta7
compiled without SMP support:
isnogud:urs$ grep SMP /usr/src/linux-2.4.3-ut/.config
# CONFIG_SMP is not set
The SCSI controller is an Adaptec AIC 7880 on an ASUS P2L97-S
mainboard (onboard). The SCSI disks are
Host: scsi0 Channel: 00 Id: 00 Lun: 00
Vendor: IBM Model: DCAS-34330W Rev: S65A
Type: Direct-Access ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 01 Lun: 00
Vendor: IBM Model: DCAS-34330W Rev: S65A
Type: Direct-Access ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 02 Lun: 00
Vendor: NEC Model: DSE2100S Rev: 0306
Type: Direct-Access ANSI SCSI revision: 02
i.e. /dev/sda and /dev/sdb are UW-SCSI and /dev/sdc is a SCSI-2 disks.
> The problem is definitely more noticable on the SCSI disks, but at least
> on the IDE disk the increased wall-clock time is wholly accounted for
> by increased system time. On the SCSI disks, it would guess that "dd"
> is waiting for I/O completions under LVM, and not on the raw disk???
How could I check? And do you have an idea, why a file system on top
of such a slow LV is, if at all, only somewhat slower?
urs
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