[Gllug] Centos 5.6 3ware raid 5

[Ken Smith]

James Courtier-Dutton wrote:
> On 8 February 2012 12:24, Ken Smith<kens at kensnet.org>  wrote:
>    
>> Hi, I didn't get any response on the Centos list so I thought I'd ask here
>> for any experience with using a 3ware raid card as a simple IDE interface.
>>
>> I've seen comments about the poor performance of these cards with raid 5
>> configs. I have an old card with 3 x 500G IDE drives connected in raid 5 and
>> I'm getting around 10mb/s write performance. :-(
>>
>> I'm seeing high iowait figures at times and associated very high cpu load
>> average figures, probably because, under load, everything is stacked up
>> waiting for the disks to actually do something.
>>
>> A non-raid sata disk in the same machine manages 70mb/s
>>
>> Does anyone know what the performance is like if I used the 3ware just as an
>> IDE controller? I could then switch to software raid5?
>>
>>      
> If it uses the megaraid driver, (not sure exactly what it is called)
> on a old Linux kernel version, then you might get problems.
> I had a number of problems with HP DL servers. More up to date Linux
> kernels use a new driver, different name, that does not seem to have
> the same problems.
> The problems I ran into where the controller pausing sometimes and
> failing to process requests. The problems were mainly with a
> combination of tape drives and disks.
> The newer driver, of a different name, fixed the problems.
> So, I would ask, which Linux kernel driver are you using.
> The output of "lspci" and "lsmod" would help.
>
> Kind Regards
>
> James
>
>    
Thanks for the replies,

Its on a 32 bit pci bus. The driver is 3w_xxxx,  (version 
1.26.03.000-2.6.18RH. )

M'board is Gigabyte P43-ES3G

Kernel is  2.6.18-238.12.1.el5.centos.plus, it's a 64 bit installation

lspci says "3ware Inc 7xxx/8xxx-series PATA/SATA-RAID"

It shares interrupts with a DVB card that isn't active when I've been 
taking measurements.

The machine has a Pentium D 3.4G CPU & 3G ram.

Top shows CPU 5 min load at around 15 when the machine is busy, sar 
shows iowait around 40% at the same time. atop shows similar readings. 
Normal cpu load is around 0.4.

I used dd to create a 1.2G file and timed it to do my write speed 
measurements. (time sh -c "dd if=/dev/zero of=ddfile bs=8k count=150000 
&& sync")

The video card is on a PCIe bus. But the machine usually runs headless 
in RL3 so the video traffic is minimal.

In terms of workload the machine runs 
sendmail/mailscanner+spamassassin+fprot/cyrus (two users, light load), 
smb, ssh, egroupware with a postgres db, local dns/dhcp, cups, apcupsd & 
Mythtv. The mysql for myth is quite busy both in terms of CPU and disk 
IO. I've been tweeking the mysql settings in my.cnf following the 
suggestions that mysqltuner is offering. The mysql db is on the raid 5 
and the video store for myth is on a separate 1.5Tb sata disk.

What drew my attention to the problem was when I copied an 8Gig file to 
the machine over the network (using smb) and the CPU load hit around 30. 
At the time, for some reason named got into an unresponsive muddle where 
it wouldn't respond to start/stop or kill commands and I ended up 
rebooting the machine. Then I started digging. I been on the trail of a 
problem where Myth becomes unresponsive occasionally and I have traced 
that to the periods of high cpu load and high iowait.

Thanks

Ken

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