Date: Mon, 17 Apr 2000 12:46:55 -0600 (MDT) From: Mark Costlow <cheeks@swcp.com> To: freebsd-scsi@FreeBSD.ORG Subject: vinum write performance Message-ID: <200004171846.MAA13065@shimi.swcp.com>
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I'm setting up a freeBSD 3.4 system on a Micron Netframe (PIII-533, 256M) with
an Adaptec SCSI controller on the motherboard (model number escapes me right
now). There are two SCSI disks connected, both are IBM DNES-318350Y's (18G,
7200 RPM). The system boots off an IDE disk.
My intention is to configure the SCSI disks as a RAID-1 mirror with vinum. I
did this successfully, however the write performance was really bad, much
worse than I expected from the papers I've read on vinum performance, so I
think I must have something configured badly.
The simple test I've been running to guage performance is 'iozone 500' (old
version of iozone that just does a sequential write followed by a sequential
read). I understand why RAID-1 writes will be slower than raw single-drive
writes, but the difference here is a factor of 7, not 2 (and with only two
drives on the bus I wouldn't expect much of a slowdown).
When I first noticed that writing to the vinum mirror volume was slow,
I thought the problem might be one or both of the disks. So I reconfigured
vinum to use just one disk (each in turn) and saw the same performance on each
one. I also put regular file system on each disk to test them and saw more
normal write performance. Here are the results of those tests:
Throuput numbers are in MB/s
iozone 500: FS Type Read Write
-------------------------------------
da0: vinum 19.3 2.2
da0: BSD 19.4 15.2
da1: vinum 18.6 2.2
da1: BSD 17.4 14.0
The newfs parameters in all cases are the system defaults. The vinum config
being used is:
drive d0 device /dev/da1s1e
volume vtest
plex name vtest.p0 org concat vol vtest
sd name vtest.p0.s0 drive d0 plex vtest.p0 len 35843405s driveoffset 265s plexoffset 0s
The write speed I see on a vinum volume with a single plex and sd is the same
as I saw with the drives in a mirror config: 2.2MB/s. As the numbers above
show, the problem isn't specific to one drive. If the writes go through
vinum, they're slow.
FWIW, regarding the recent discussion about the drive's write cache: the write
cache is enabled on these drives.
If anyone has any ideas what I might be doing wrong, or if I've left out any
useful configuration information, please let me know. Thanks,
Mark
--
Mark Costlow | Southwest Cyberport | Fax: +1-505-232-7975
cheeks@swcp.com | Web: www.swcp.com | Voice: +1-505-232-7992
"Education is never a waste" - Viscount du Valmont
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