Re: [CentOS-virt] SATA vs RAID5 vs VMware

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I have been using a 3ware 9690se sata card with raid5.  I have been running Centos using xen and have had no problems.
I wrote my virtual machines to the raw raid5 drive.  Its seems to have worked fine for me.

On Thu, Sep 24, 2009 at 9:18 PM, Philip Gwyn <liste@xxxxxxxxxxxxx> wrote:
Hello,

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
stutters.

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" :
  http://www.awale.qc.ca/vmware/vmstat.txt
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,

-Philip


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