slow scsi disk perf (sym53c875 and IBM drives)
Quoted 9 lines
I've been having relatively poor scsi disk performance for as long as I can remember now. I've experienced this with ~2.2.12 all the way up to 2.4.17.
I'm not much of a scsi buff but I've read some suggestions such as proper termination, queue depths, etc but nothing seems to have helped. My understanding is that I should be getting better performance than I'm getting with these drives.
I have a few DCHS UW disks and get about 10 MB/sec on a streaming read from them (slower toward the end of the disk). You can make your own measurements bypassing the block subsystem (and sd) with the sg_dd utility found in sg3_utils package. That package is now listed on freshmeat.net .
For example:
$ time sg_dd if=/dev/sg0 of=/dev/null bs=512 count=2M to time a 1GB (approx) read at the start of the disk. [Use sg_map to work out the mapping between the "sd" and "sg" device names.]
If there is a major discrepancy between this figure and what you are seeing from hdparm then there is a problem.
On the disk in this box (Seagate ST318451LW 15Krpm) I get:
hdparm -t /dev/sda
/dev/sda:
Timing buffered disk reads: 64 MB in 1.99 seconds = 32.16 MB/sec
In my sg_dd tests I get better than 40 MB/sec. The hdparm test definitely was timing extraneous activity because the disk light was not on all the time.
Quoted 3 lines
Any suggestions would be appreciated and if this is not the right forum to ask.. please direct me to the proper place.
[email protected] is arguably a more appropriate newsgroup.
Doug Gilbert
Rest of original post [for the linux-scsi list] vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv hdparm output:
/dev/sda:
Timing buffered disk reads: 64 MB in 10.94 seconds = 5.85 MB/sec
/dev/sdb:
Timing buffered disk reads: 64 MB in 8.66 seconds = 7.39 MB/sec
/dev/sdc:
Timing buffered disk reads: 64 MB in 10.88 seconds = 5.88 MB/sec
SCSI subsystem driver Revision: 1.00
sym53c8xx: at PCI bus 0, device 12, function 0
sym53c8xx: setting PCI_COMMAND_PARITY...(fix-up)
sym53c8xx: 53c875 detected with Symbios NVRAM
sym53c875-0: rev 0x26 on pci bus 0 device 12 function 0 irq 10
sym53c875-0: Symbios format NVRAM, ID 7, Fast-20, Parity Checking
sym53c875-0: on-chip RAM at 0xe0502000
sym53c875-0: restart (scsi reset).
sym53c875-0: Downloading SCSI SCRIPTS.
scsi0 : sym53c8xx-1.7.3c-20010512
sym53c875-0-<0,*>: FAST-10 WIDE SCSI 20.0 MB/s (100.0 ns, offset 15)
Vendor: IBM Model: DCHS09W Rev: 6363
Type: Direct-Access ANSI SCSI revision: 02
sym53c875-0-<1,*>: FAST-20 WIDE SCSI 40.0 MB/s (50.0 ns, offset 15)
Vendor: IBM Model: DGHS09U Rev: 03E0
Type: Direct-Access ANSI SCSI revision: 03
sym53c875-0-<4,*>: FAST-10 WIDE SCSI 20.0 MB/s (100.0 ns, offset 15)
Vendor: IBM Model: DCHS09W Rev: 6363
Type: Direct-Access ANSI SCSI revision: 02
sym53c875-0-<0,0>: tagged command queue depth set to 8 sym53c875-0-<1,0>: tagged command queue depth set to 8 sym53c875-0-<4,0>: tagged command queue depth set to 8 Attached scsi disk sda at scsi0, channel 0, id 0, lun 0 Attached scsi disk sdb at scsi0, channel 0, id 1, lun 0 Attached scsi disk sdc at scsi0, channel 0, id 4, lun 0 SCSI device sda: 17774160 512-byte hdwr sectors (9100 MB) Partition check:
sda: sda1 < sda5 sda6 sda7 >
SCSI device sdb: 17774160 512-byte hdwr sectors (9100 MB)
sdb: sdb1 sdb2
SCSI device sdc: 17774160 512-byte hdwr sectors (9100 MB)
sdc: sdc1