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On this system there is a lot of "await" which is causing slow response. i need to find out which disk behind the LSI logical volume is slowing it down...

IBM blade, 2 HDD with LSI RAID (LV simple mirror) on top. On top of that is RHEL LVM.

..devices...

# lsscsi
[0:0:0:0]    disk    IBM-ESXS ST9146852SS      B62C  -
[0:0:1:0]    disk    IBM-ESXS ST9146852SS      B62C  -
[0:1:3:0]    disk    LSILOGIC Logical Volume   3000  /dev/sda

...RHEL LVM...

# pvdisplay -v
    Scanning for physical volume names
  --- Physical volume ---
  PV Name               /dev/sda2
  VG Name               VolGroup00
  PV Size               135.48 GB / not usable 13.20 MB
  Allocatable           yes
  PE Size (KByte)       32768

disk latency...

so for this iostat output, how do i know which device in LSI LV is causing delays?

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.19    0.00    0.16    8.41    0.00   91.25

Device:         rrqm/s   wrqm/s   r/s   w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sda               0.00     4.00  0.00 12.50     0.00   272.00    21.76     7.01 1317.20  80.00 100.00
sda1              0.00     0.00  0.00  0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
sda2              0.00     4.00  0.00 12.50     0.00   272.00    21.76     7.01 1317.20  80.00 100.00
dm-0              0.00     0.00  0.00  0.50     0.00     4.00     8.00    10.48 62549.00 1358.00  67.90
dm-1              0.00     0.00  0.00  0.00     0.00     0.00     0.00     0.45    0.00   0.00  44.50
dm-2              0.00     0.00  0.00  5.50     0.00    44.00     8.00     2.85  898.00 167.64  92.20
dm-3              0.00     0.00  0.00  1.50     0.00    12.00     8.00     0.86  573.67 336.00  50.40
dm-4              0.00     0.00  0.00  0.50     0.00     4.00     8.00     2.41 5162.00 1610.00  80.50
dm-5              0.00     0.00  0.00  0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
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how do i know which device in LSI LV is causing delays?

From only that output, you don't.

You'll need to query the HW RAID controller for more information, and for that, you'll need a specific tool, and the correct tool depends on the exact model of the RAID controller. The outputs of lsscsi -H and/or lspci -nn might be helpful here.

If the kernel module that drives the RAID controller is named megaraid_sas, then the tool you need would be storcli, or megacli[64], which can be tricky to find unless you know that the intellectual property that was once LSI's is currently in hands of Broadcom.

On the other hand, if the kernel module is mptsas, then you would need mpt-status, CFGGEN or perhaps lsiutil which is notoriously hard to find.

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