[CentOS-virt] SATA vs RAID5 vs VMware

Fri Sep 25 01:18:42 UTC 2009
Philip Gwyn <liste at artware.qc.ca>


I have strange behaviour on a server that I can't get a handle on.  I have a
reasonably powerful server running VMware server 1.0.4-56528.  It has a RAID5
build with mdadm on 5 SATA drives.  Masses of ram and 2 XEON CPUs.  But it

Example : fire up vi, press and keep finger on i.  After filling 2-3 lines, the
display is stopped for 2-12 seconds.  Then they continue.  This happens even on
the host OS, at the console.

Host system running CentOS 5.2 x86-64:

  CPU : 2x Xeon E5430 @ 2.66GHz
  RAM : 24GB
 Mobo : DSBV-DX
   HD : 5 x SATA ST3750330AS 750GB in RAID5

There are 5 VMs, detailed at http://www.awale.qc.ca/vmware/stj1.txt to make
this mail shorter.

Seems to me this system should be more then adequate to handle the load.  

This is what vmstat on the host looks like when the server is "unhappy" :
Spending a lot of time in 'wa', but 'bo' and 'bi' are miniscule.

The problem seems like a disk problem.  I grow to suspect that SATA isn't ready
for the big time.  I also grow to dislike RAID5.

Questions :

- Anyone have a clue or other on how to track down my bottle neck?

- SATA NCQ is limited to 15 queue depth.  Is this per-SATA-port or
  per-SATA-chip? Or does this question make no sense?

- I realise there are more recent versions of CentOS out.  Are there specific
  items in the changelogs that would affect my problem?

Thank you for any help,