| View previous topic :: View next topic |
| Author |
Message |
Spack
n00b
Joined: 02 Feb 2003
Posts: 32
|
 Posted: Thu Apr 22, 2004 5:34 am Post subject: SATA + Software RAID Performance Doesn't Add Up |
 |
|
I just recently moved back to Gentoo after a years abscence. I don't often post here, usually only search and read.
I am currently running gentoo-dev-sources 2.6.3. I have a Promise PDC20376 SATA/RAID controller onboard:
| Code: |
# cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
Vendor: ATA Model: ST380013AS Rev: 1.00
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi1 Channel: 00 Id: 00 Lun: 00
Vendor: ATA Model: ST380013AS Rev: 1.00
Type: Direct-Access ANSI SCSI revision: 05
|
and wanted to stripe them for performance:
| Code: |
# cat /proc/mdstat
Personalities : [raid0] [raid1]
md1 : active raid0 sdb3[1] sda3[0]
155701760 blocks 32k chunks
md0 : active raid1 sdb1[1] sda1[0]
40064 blocks [2/2] [UU]
unused devices: <none>
|
However, I don't seem to be getting the preformance benefit I would expect from the stripped drives:
| Code: |
# hdparm -tT /dev/sda
/dev/sda:
Timing buffer-cache reads: 892 MB in 2.01 seconds = 444.73 MB/sec
Timing buffered disk reads: 152 MB in 3.05 seconds = 49.78 MB/sec
|
| Code: |
# hdparm -tT /dev/md1
/dev/md1:
Timing buffer-cache reads: 888 MB in 2.01 seconds = 442.74 MB/sec
Timing buffered disk reads: 168 MB in 3.01 seconds = 55.84 MB/sec
|
Can anyone shed some light on why my performance might be like this? Am I missing something basic?
_________________
Gentoo 2004.4
Gnome 2.8
Athlon XP 1800+ 512MB DDR
Promise SATA |
|
| Back to top |
|
 |
Spack
n00b
Joined: 02 Feb 2003
Posts: 32
|
| Posted: Sat Apr 24, 2004 8:59 am Post subject: |
|
|
Bump. So no one's got any ideas?
_________________
Gentoo 2004.4
Gnome 2.8
Athlon XP 1800+ 512MB DDR
Promise SATA |
|
| Back to top |
|
|
Crg
Guru
Joined: 29 May 2002
Posts: 345
Location: London
|
| Posted: Sat Apr 24, 2004 11:29 am Post subject: |
|
|
| Spack wrote: | | Bump. So no one's got any ideas? |
What does hdparm -t /dev/sdb show? |
|
| Back to top |
|
|
Spack
n00b
Joined: 02 Feb 2003
Posts: 32
|
| Posted: Sat Apr 24, 2004 12:42 pm Post subject: |
|
|
| Code: | # hdparm -tT /dev/sdb
/dev/sdb:
Timing buffer-cache reads: 900 MB in 2.01 seconds = 448.50 MB/sec
Timing buffered disk reads: 168 MB in 3.03 seconds = 55.44 MB/sec
|
_________________
Gentoo 2004.4
Gnome 2.8
Athlon XP 1800+ 512MB DDR
Promise SATA |
|
| Back to top |
|
|
Spack
n00b
Joined: 02 Feb 2003
Posts: 32
|
| Posted: Tue Aug 17, 2004 11:02 pm Post subject: |
|
|
I've been thinking further about this and I think I might have an answer as to why this is. I ahve two partitions on each physical drive. One partition from each drive is used in a raid 0 configuration for /boot (md0) and the other partition for each drive is in a raid 1 configuration for / (md1).
Is it possible that beacuse I have the md0 in mirror mode this is preventing the md1 (striped) from achieving the performance its capable of?
i.e. if I changed md0 to striped also would the performance change?
I'm keen to try but want to know I'm going down the right path first.
_________________
Gentoo 2004.4
Gnome 2.8
Athlon XP 1800+ 512MB DDR
Promise SATA |
|
| Back to top |
|
|
Nate_S
Guru
Joined: 18 Mar 2004
Posts: 414
|
| Posted: Tue Aug 17, 2004 11:42 pm Post subject: |
|
|
| you may be on the right track there. I always thought you stripe the devices first, then make partitions on top of that, not the other way around. YMMV |
|
| Back to top |
|
|
sindre
Guru
Joined: 01 Nov 2002
Posts: 315
Location: Norway
|
| Posted: Tue Aug 17, 2004 11:42 pm Post subject: |
|
|
I doubt that would work. I've got the same problem, but on P-ATA. I think it's just my IDE-controller sucking though.
/dev/hda and /dev/hdc is set up in raid0 md0.
hdparm -t /dev/hda : about 50MB/s
hdparm -t /dev/hdc : about 50MB/s
hdparm -t /dev/md0 : about 55MB/s
hparm -t /dev/hda & hdparm -t /dev/hdc : about 28 MB/s each.
So maybe my ICH4 intel integrated ide controller can't manage full speed on both IDE buses at the same time? I'd appreciate if anyone with good rad0 scores could do the same test. Anyone know how much overhead in terms of latency and cpu% software raid0 gives? Maybe I'm better off without. |
|
| Back to top |
|
|
Spack
n00b
Joined: 02 Feb 2003
Posts: 32
|
| Posted: Wed Aug 18, 2004 2:30 am Post subject: |
|
|
| Nate_S wrote: | | you may be on the right track there. I always thought you stripe the devices first, then make partitions on top of that, not the other way around. YMMV |
Well yes that is the normal approach with hardware raid however this is using linux software raid. Although I have an onboard Promise 20376 raid controller the software raid is generally recommended as the performance difference is minimal and the software raid is easier to implement.
_________________
Gentoo 2004.4
Gnome 2.8
Athlon XP 1800+ 512MB DDR
Promise SATA |
|
| Back to top |
|
|
XioXouS
n00b
Joined: 01 Apr 2005
Posts: 59
|
| Posted: Fri Apr 01, 2005 7:17 pm Post subject: |
|
|
After much searching I came across a solution
blockdev --setra 4096 /dev/sda
blockdev --setra 4096 /dev/sdb
blockdev --setra 4096 /dev/md1
Hope that helps you too. |
|
| Back to top |
|
|
jmahler
n00b
Joined: 30 Mar 2004
Posts: 42
|
| Posted: Thu Apr 07, 2005 6:31 pm Post subject: |
|
|
| XioXouS wrote: | After much searching I came across a solution
blockdev --setra 4096 /dev/sda
blockdev --setra 4096 /dev/sdb
blockdev --setra 4096 /dev/md1
Hope that helps you too. |
How does one make that a permanent change? it seems to go away after a reboot. |
|
| Back to top |
|
|
smithjd15
Tux's lil' helper
Joined: 12 Mar 2003
Posts: 130
Location: Edmonton, AB, CA
|
| Posted: Thu Apr 07, 2005 8:52 pm Post subject: |
|
|
| Quote: | | How does one make that a permanent change? it seems to go away after a reboot. |
Better question...what does it do?  |
|
| Back to top |
|
|
XioXouS
n00b
Joined: 01 Apr 2005
Posts: 59
|
| Posted: Sun Apr 10, 2005 8:24 pm Post subject: |
|
|
/etc/conf.d/local is a good place for personal customizations like that
man blockdev
this particular command sets the readahead amount higher in the hopes that it will get a little more usable data at a time and not need to access the disk again for a bit, of course it doesn't work very well if the things you wanted weren't in order on the disk, and I don't believe hdparm checks that very well
i've heard, but not tested yet, that bonnie++ is a better way to measure actual performance
did it work for you too, in terms of hdparm -Tt results? |
|
| Back to top |
|
|
|
Kernel & Hardware
