[Lustre-discuss] xserve raid

Brock Palen brockp at umich.edu
Thu Oct 18 10:02:19 PDT 2007


On Oct 18, 2007, at 4:42 AM, Andreas Dilger wrote:

> On Oct 17, 2007  15:35 -0400, Brock Palen wrote:
>> We are doing some testing,
>>
>> For a OST with a xserve raid connected to linux,  is it better to not
>> have a partition table
>>
>> mkfs.lustre /dev/sda
>>
>> or to have a partition?
>> fdisk /dev/sda
>> mkfs.lustre /dev/sda1
>
> For RAID 5/6 devices we recommend NOT having a partition table.   
> The reason
> is that the partition table offsets the data partitions by a small  
> amount
> (512 bytes usually) and this causes writes to span multiple RAID  
> chunks and
> unnecessary read-modify-write activity.
>
> For best performance, pick a RAID chunk size that divides evenly into
> 1MB (e.g. 4 or 8 data disks + parity).  The ldiskfs mballoc code works
> to align the allocation with the RAID chunk size for best performance.

Thanks I will keep this in mind.

I did some basics test,  1MDS 1OST 1raid5 (half a xserve raid)  Using  
tiobench on 1 client,  using no partition table netted about 5MB/s  
faster for streaming read/write.  I will scale up my tests though and  
try some other raid configurations.  Thanks for the help.

>
> Cheers, Andreas
> --
> Andreas Dilger
> Principal Software Engineer
> Cluster File Systems, Inc.
>
>
>




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