Re: Ext3 meta-data performance

Kevin Jacobs (jacobs@penguin.theopalgroup.com)
Fri, 30 May 2003 06:09:02 -0400 (EDT)


On Thu, 29 May 2003, Nick Piggin wrote:
> Kevin Jacobs wrote:
> >[...]
> >Since these rsync backups are done in addition to traditional daily tape
> >backups, we've taken the system out of production use and opened the door
> >for experimentation. So, the next logical step was to try a 2.5 kernel.
> >After some work, I've gotten 2.5.70-mm2 booting and it is _much_ better than
> >the Redhat 2.4 kernels, and the system interactivity is flawless. However,
> >the speed of creating hard-links is still three and a half times slower than
> >with the old 2.2 kernel. It now takes ~14 minutes to create the links, and
> >from what I can tell, the bottlenecks is not the CPU or the disk-throughput.
> >
> Its probably seek bound.
> Provide some more information about your disk/partition setup, and external
> journals, and data= mode. Remember ext3 will generally always have to do
> more work than ext2.

SCSI ID 1 3ware 7500-8 ATA RAID Controller

* Array Unit 0 Mirror (RAID 1) 40.01 GB OK
+ Port 0 WDC WD400BB-00DEA0 40.02 GB OK
+ Port 1 WDC WD400BB-00DEA0 40.02 GB OK
* Array Unit 4 Striped with Parity 64K (RAID 5) 555.84 GB OK
+ Port 4 IC35L180AVV207-1 185.28 GB OK
+ Port 5 IC35L180AVV207-1 185.28 GB OK
+ Port 6 IC35L180AVV207-1 185.28 GB OK
+ Port 7 IC35L180AVV207-1 185.28 GB OK

Disk /dev/sda: 40.0 GB, 40019615744 bytes
255 heads, 63 sectors/track, 4865 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sda1 * 1 261 2096451 83 Linux
/dev/sda2 262 1566 10482412+ 83 Linux
/dev/sda3 1567 4570 24129630 83 Linux
/dev/sda4 4571 4865 2369587+ f Win95 Ext'd (LBA)
/dev/sda5 4571 4589 152586 83 Linux
/dev/sda6 4590 4734 1164681 83 Linux
/dev/sda7 4735 4865 1052226 83 Linux

Disk /dev/sdb: 555.8 GB, 555847581696 bytes
255 heads, 63 sectors/track, 67577 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sdb1 * 1 67577 542812221 83 Linux

Unit 0 is /dev/sda and the journal is /dev/sda5. Unit 1 is /dev/sdb and the
backup filesystem is /dev/sdb1. The data= mode is whatever is default,
/dev/sdb1 is mounted noatime. I've also applied the journal_refile_buffer
patch posted by AKPM yesterday morning.

> If you want to play with the scheduler, try set
> /sys/block/blockdev*/queue/nr_requests = 8192

This killed the entire system -- livelocking it with no disk activity to the
point that I had to hit the reset button. So does setting nr_requests on
sda and sdb from 128 to 256. The problems hit before the rsync, during a
'rm -Rf' on a previously copied tree.

> then try
> /sys/block/blockdev*/queue/iosched/antic_expire = 0

This seemed to make no difference.

> Try the above combinations with and without a big TCQ depth. You should
> be able to set them on the fly and see what happens to throughput during
> the operation. Let me know what you see.

I'm not sure how to change TCQ depth on the fly. Last I knew, it was a
compiled-in parameter.

I have some more time to experiment, so please let me know if there is
anything else you think I should try.

Thanks,
-Kevin

-- 
--
Kevin Jacobs
The OPAL Group - Enterprise Systems Architect
Voice: (216) 986-0710 x 19         E-mail: jacobs@theopalgroup.com
Fax:   (216) 986-0714              WWW:    http://www.theopalgroup.com

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