[CentOS] Poor RAID performance new Xeon server?

Ross Walker rswwalker at gmail.com
Sun Jan 11 17:36:05 UTC 2009


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.

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

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.

-Ross
  


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