[CentOS] Poor RAID performance new Xeon server?

Stewart Williams lists at pinkyboots.co.uk
Sun Jan 11 18:06:20 UTC 2009


Ross Walker wrote:
> On Jan 11, 2009, at 10:13 AM, Stewart Williams  
> <lists at pinkyboots.co.uk> wrote:
> 
>> William Warren wrote:
>>> Stewart Williams wrote:
>>>> I have just purchased an HP ProLiant HP ML110 G5 server and  
>>>> install ed
>>>> CentOS 5.2 x86_64 on it.
>>>>
>>>> It has the following spec:
>>>>
>>>> Intel(R) Xeon(R) CPU 3065  @ 2.33GHz
>>>> 4GB ECC memory
>>>> 4 x 250GB SATA hard disks running at 1.5GB/s
>>>>
>>>> Onboard RAID controller is enabled but at the moment I have used  
>>>> mdadm
>>>> to configure the array.
>>>>
>>>> RAID bus controller: Intel Corporation 82801 SATA RAID Controller
>>>>
>>>> For a simple striped array I ran:
>>>>
>>>> # mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sdb1 / 
>>>> dev/sdc1
>>>> # mke2fs -j /dev/md0
>>>> # mount -t ext3 /dev/md0 /mnt
>>>>
>>>> Attached are the results of 2 bonnie++ tests I made to test the
>>>> performance:
>>>>
>>>> # bonnie++ -s 256m -d /mnt -u 0 -r 0
>>>>
>>>> and
>>>>
>>>> # bonnie++ -s 1g -d /mnt -u 0 -r 0
>>>>
>>>> I also tried 3 of the drives in a RAID 5 setup with gave similar  
>>>> results.
>>>>
>>>> Is it me or are the results poor?
>>>>
>>>> Is this the best I can expect from the hardware or is something  
>>>> wrong?
>>>>
>>>> I would appreciate any advice or possible tweaks I can make to the
>>>> system to make the performance better.
>>>>
>>>> The block I/O is the thing that concerns me as mostly I am serving a
>>>> 650MB file via samba to 5 clients and I think this is where I need  
>>>> the
>>>> speed.
>>>>
>>>> Plus I am hoping to run some virtualised guests on it eventually,  
>>>> but
>>>> nothing too heavy.
>>>>
>>>> --- 
>>>> --- 
>>>> ------------------------------------------------------------------
>>>>
>>>> _______________________________________________
>>>> CentOS mailing list
>>>> CentOS at centos.org
>>>> http://lists.centos.org/mailman/listinfo/centos
>>> That onbard raid is fakeraid..so when you dialup raid 5 you  
>>> effectivly
>>> put hte hdd's in pio mode since ALL data has to be routed through  
>>> your
>>> cpu.  Please get a raid card from HP or go get a 3ware card so you  
>>> ahve
>>> real hardware raid.
>>>
>>> fake and real raid chpsets:
>>> http://linuxmafia.com/faq/Hardware/sata.html
>>>
>>> Why using fakeraid at all is bad:
>>> http://thebs413.blogspot.com/2005/09/fake-raid-fraid-sucks-even-more-at.html
>>>
>>> MDM under linux is kernel raid that does not use a binary
>>> driver..however you don't want to do ANY software raid 5.
>> Thanks William,
>>
>> I am no expert on RAID, so you have opened my eyes to somethings I
>> wasn't aware of.
>>
>> I am considering disabling the onboard RAID in the BIOS and
>> re-installing CentOS and configuring the 4 drives as RAID 10 just to  
>> see
>> what the performance is like.
>>
>> Or I may purchase a card as you advise. Would I benefit from buying a
>> SCSI/or SAS card and drives for my requirements? Basically the main  
>> role
>> of the machine is to serve a ~600MB file via samba to 5 Windows XP  
>> cient
>> PC's on a gigabit network.
> 
> If all your doing is serving a single file to a handful of PCs then a  
> 2 drive mirror will be more then enough.

That is what I currently have setup on the old server, but it only has 
1GB ram and AMD Duron 1300MHz CPU.

The performance on the clients gets slower as the file size grows and 
now it has got very slow - hence the new server.

> 
> You should stick with the OS RAID though as the onboard RAID will  
> bring nothing but pain.

That is what I have read. So understood :-)

> 
> For sequential IO expect 60MB/s read and 40MB/s write (with the  
> drive's write cache enabled) per drive. Random IO is an order of  
> magnitude less.

Should that be OK for my needs or for the clients to be happy should I 
be wanting more? what figure should I be looking at?

> 
> -Ross

Sorry for all the questions and thanks for the help.

Stewart


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