Disk saturation

Hi,

One of our database server is getting some very high response times and I´m
wondering what can be responsible for this issue.

A strange behaviour in this server is the saturation number iostat is
giving, an average of 20% for only 140 wkB/s or can I consider them normal
numbers?

It is a Fedora Core release 4 (Stentz) box with 4 GB RAM and 2 GenuineIntel
XEON CPU 3.20 GHz Cache: 1024 KB. In the disk subsystem we have two SCSI
drives in hardware RAID1.

Some typical iostat -x data:
cpu-moy: %user %nice %sys %iowait %idle
11,96 0,00 7,04 1,31 79,70

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s
avgrq-sz avgqu-sz await svctm %util
sda 0,00 30,44 0,81 3,43 14,52 270,97 7,26 135,48
67,43 0,19 46,05 7,29 3,08

cpu-moy: %user %nice %sys %iowait %idle
12,26 0,00 7,34 6,63 73,77

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s
avgrq-sz avgqu-sz await svctm %util
sda 0,00 32,26 0,00 4,41 0,00 293,39 0,00 146,69
66,55 1,51 342,32 25,14 11,08

cpu-moy: %user %nice %sys %iowait %idle
13,67 0,00 6,83 7,74 71,76

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s
avgrq-sz avgqu-sz await svctm %util
sda 0,00 31,99 0,00 3,82 0,00 286,52 0,00 143,26
74,95 2,93 767,58 55,84 21,35

cpu-moy: %user %nice %sys %iowait %idle
13,27 0,00 6,83 14,37 65,53

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s
avgrq-sz avgqu-sz await svctm %util
sda 0,00 31,73 0,00 4,02 0,00 285,94 0,00 142,97
71,20 2,73 680,40 49,25 19,78

cpu-moy: %user %nice %sys %iowait %idle
12,86 0,00 6,33 9,45 71,36

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s
avgrq-sz avgqu-sz await svctm %util
sda 0,00 30,92 0,00 3,41 0,00 274,70 0,00 137,35
80,47 2,33 681,35 57,53 19,64

cpu-moy: %user %nice %sys %iowait %idle
12,45 0,00 6,02 1,91 79,62

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s
avgrq-sz avgqu-sz await svctm %util
sda 0,00 33,00 0,60 4,23 6,44 297,79 3,22 148,89
63,00 0,41 85,29 20,00 9,66

dmesg data:
....
....
SCSI subsystem initialized
Fusion MPT base driver 3.01.20
Copyright (c) 1999-2004 LSI Logic Corporation
ACPI: PCI Interrupt 0000:02:04.0[A] -> GSI 42 (level, low) -> IRQ 185
mptbase: Initiating ioc0 bringup
ioc0: 53C1030: Capabilities={Initiator,Target}
Fusion MPT SCSI Host driver 3.01.20
scsi0 : ioc0: LSI53C1030, FwRev=01032300h, Ports=1, MaxQ=255, IRQ=185
input: AT Translated Set 2 keyboard on isa0060/serio0
input: AT Translated Set 2 keyboard on isa0060/serio0
megaraid cmm: 2.20.2.5 (Release Date: Fri Jan 21 00:01:03 EST 2005)
megaraid: 2.20.4.5 (Release Date: Thu Feb 03 12:27:22 EST 2005)
megaraid: probe new device 0x1000:0x1960:0x1028:0x0520: bus 2:slot 5:func 0
ACPI: PCI Interrupt 0000:02:05.0[A] -> GSI 37 (level, low) -> IRQ 193
megaraid: fw version:[351S] bios version:[1.10]
scsi1 : LSI Logic MegaRAID driver
scsi[1]: scanning scsi channel 0 [Phy 0] for non-raid devices
Vendor: SDR Model: GEM318P Rev: 1
Type: Processor ANSI SCSI revision: 02
scsi[1]: scanning scsi channel 1 [virtual] for logical drives
Vendor: MegaRAID Model: LD 0 RAID1 69G Rev: 351S
Type: Direct-Access ANSI SCSI revision: 02
SCSI device sda: 143114240 512-byte hdwr sectors (73274 MB)
sda: asking for cache data failed
sda: assuming drive cache: write through
SCSI device sda: 143114240 512-byte hdwr sectors (73274 MB)
sda: asking for cache data failed
sda: assuming drive cache: write through
sda: sda1 sda2 sda3 sda4 < sda5 >
Attached scsi disk sda at scsi1, channel 1, id 0, lun 0
libata version 1.10 loaded.
ata_piix version 1.03
ACPI: PCI Interrupt 0000:00:1f.2[A] -> GSI 18 (level, low) -> IRQ 177
PCI: Setting latency timer of device 0000:00:1f.2 to 64
ata1: SATA max UDMA/133 cmd 0xBC98 ctl 0xBC92 bmdma 0xBC60 irq 177
ata2: SATA max UDMA/133 cmd 0xBC80 ctl 0xBC7A bmdma 0xBC68 irq 177
ata1: SATA port has no device.
scsi2 : ata_piix
ata2: SATA port has no device.
scsi3 : ata_piix
isa bounce pool size: 16 pages
kjournald starting. Commit interval 5 seconds
EXT3-fs: mounted filesystem with ordered data mode.
SELinux: Disabled at runtime.
SELinux: Unregistering netfilter hooks
cfq: depth 4 reached, tagging now on
Attached scsi generic sg0 at scsi1, channel 0, id 6, lun 0, type 3
Attached scsi generic sg1 at scsi1, channel 1, id 0, lun 0, type 0
Floppy drive(s): fd0 is 1.44M
...
...
...

Thank you in advance!

Reimer

Reimer
carlos(dot)reimer(at)opendb(dot)com(dot)br
OpenDB Serviços e Treinamentos PostgreSQL e DB2
Fone: 47 3327-0878 Cel: 47 9183-0547
www.opendb.com.br