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Old 10-10-2006, 04:21 PM   #1
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MD Raid5 Performance issue

We are currently running a fileserver to host lots of small images on a server running slackware 10.2 and md raid.

The raidset is made up by eight 300Gb sata disks where seven is in the set and one spare.

The problem we are having is that the drive starts to pause write requests when the load is high. We have steady stream at about 600Kb/s writes but the disks can't handle it.

We have a lot of read requests which complete without any delay.

I don't know much about configuring software raid and I hope that I have missed something that can make writes get more priority or maybe buffer writes somehow.

Below i attach lspci and a snapshot of iostat.

Greatful for any help or insight,

This is a typical output of iostat while four programs are trying to write to the array.

Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
hda 97.00 7992.00 0.00 7992 0
sda 41.00 1264.00 0.00 1264 0
sdb 51.00 1008.00 0.00 1008 0
sdc 54.00 1600.00 0.00 1600 0
sdd 47.00 832.00 0.00 832 0
sde 48.00 840.00 0.00 840 0
sdf 29.00 576.00 0.00 576 0
sdg 40.00 616.00 0.00 616 0
sdh 0.00 0.00 0.00 0 0
md0 298.00 6784.00 0.00 6784 0

00:00.0 Memory controller: nVidia Corporation CK804 Memory Controller (rev a4)
00:01.0 ISA bridge: nVidia Corporation CK804 ISA Bridge (rev a4)
00:01.1 SMBus: nVidia Corporation CK804 SMBus (rev a2)
00:02.0 USB Controller: nVidia Corporation CK804 USB Controller (rev a2)
00:02.1 USB Controller: nVidia Corporation CK804 USB Controller (rev a4)
00:06.0 IDE interface: nVidia Corporation CK804 IDE (rev f3)
00:07.0 IDE interface: nVidia Corporation CK804 Serial ATA Controller (rev f3)
00:08.0 IDE interface: nVidia Corporation CK804 Serial ATA Controller (rev f3)
00:09.0 PCI bridge: nVidia Corporation CK804 PCI Bridge (rev a2)
00:0a.0 Bridge: nVidia Corporation CK804 Ethernet Controller (rev a3)
00:0b.0 PCI bridge: nVidia Corporation CK804 PCIE Bridge (rev a3)
00:0c.0 PCI bridge: nVidia Corporation CK804 PCIE Bridge (rev a3)
00:0d.0 PCI bridge: nVidia Corporation CK804 PCIE Bridge (rev a3)
00:0e.0 PCI bridge: nVidia Corporation CK804 PCIE Bridge (rev a3)
00:18.0 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] HyperTransport Technology Configuration
00:18.1 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] Address Map
00:18.2 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] DRAM Controller
00:18.3 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] Miscellaneous Control
01:00.0 VGA compatible controller: nVidia Corporation GeForce 6200 TurboCache(TM) (rev a1)
05:0a.0 RAID bus controller: Silicon Image, Inc. SiI 3114 [SATALink/SATARaid] Serial ATA Controller (rev 02)
05:0c.0 Ethernet controller: Marvell Technology Group Ltd. 88E8001 Gigabit Ethernet Controller (rev 13)
Old 10-11-2006, 09:30 AM   #2
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If performance is a requirement, then you would be best serverd to get a Hardware RAID controller.

Check 3Ware for Hardware controllers that are well supported under Linux.

Odds are your onboard controllers don't support features such as NCQ (Native Command Queueing
Hot swap support
Online array expansion
lower CPU Utilization
etc.. etc.. etc..

There are other benefits of a hardware based solution.

So frankly for an array that size I wouldn't mess with Software based RAID.


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