Re: Poor performance on seq scan

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On 13-Sep-06, at 6:16 AM, Laszlo Nagy wrote:


I have had extremely bad performance historically with onboard SATA chipsets on Linux. The one exception has been with the Intel based chipsets (not the
CPU, the I/O chipset).

This board has Intel chipset. I cannot remember the exact type but it was not in the low end category.
dmesg says:

<Intel ICH7 SATA300 controller>
kernel: ad4: 152626MB <SAMSUNG HD160JJ ZM100-33> at ata2-master SATA150 kernel: ad4: 152627MB <SAMSUNG HD160JJ ZM100-33> at ata3-master SATA150

It is very likely that you are having problems with the driver for the
chipset.

Are you running RAID1 in hardware? If so, turn it off and see what the
performance is.  The onboard hardware RAID is worse than useless, it
actually slows the I/O down.

I'm using software raid, namely gmirror:

GEOM_MIRROR: Device gm0 created (id=2574033628).
GEOM_MIRROR: Device gm0: provider ad4 detected.
GEOM_MIRROR: Device gm0: provider ad6 detected.
GEOM_MIRROR: Device gm0: provider ad4 activated.
GEOM_MIRROR: Device gm0: provider ad6 activated.

#gmirror list
Geom name: gm0
State: COMPLETE
Components: 2
Balance: round-robin
Slice: 4096
Flags: NONE
GenID: 0
SyncID: 1
ID: 2574033628
Providers:
1. Name: mirror/gm0
  Mediasize: 160040803328 (149G)
  Sectorsize: 512
  Mode: r5w5e6
Consumers:
1. Name: ad4
  Mediasize: 160040803840 (149G)
  Sectorsize: 512
  Mode: r1w1e1
  State: ACTIVE
  Priority: 0
  Flags: DIRTY
  GenID: 0
  SyncID: 1
  ID: 1153981856
2. Name: ad6
  Mediasize: 160041885696 (149G)
  Sectorsize: 512
  Mode: r1w1e1
  State: ACTIVE
  Priority: 0
  Flags: DIRTY
  GenID: 0
  SyncID: 1
  ID: 3520427571


I tried to do:

#sysctl vfs.read_max=32
vfs.read_max: 6 -> 32

but I could not reach better disk read performance.

Thank you for your suggestions. Looks like I need to buy SCSI disks.

Well before you go do that try the areca SATA raid card

Regards,

  Laszlo


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