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Re: Anaconda/installer aligning partitions during install and SAN performance



On Wed, Jun 06, 2007 at 02:30:24PM +0300, Pasi Kärkkäinen wrote:
> Hi!
> 
> When anaconda initializes a disk and creates a new partition (the default partition layout),
> the first partition is set to start from the sector 63. 
> 
> In normal cases and with normal harddisks this is fine. 
> 
> But if your disk is a SAN LUN (iSCSI, FC), this could cause all the IO to be
> "misaligned", causing a performance drop. Many SAN arrays want the partitions
> to be aligned on a 8 kB boundary, or some even on 64 kB boundary. 
> 
> Would it cause problems if anaconda automatically aligns partitions to start 
> from a sector that is a multiple of 8 (or even 64 kB) ? Or maybe add an option 
> to specify how to align the partitions? 
> 
> VMware document about aligning partitions for ESX/VMFS for optimal
> performance: 
> 
> http://www.vmware.com/pdf/esx3_partition_align.pdf
> 

And more about the performance gains when aligning partitions (from the pdf
above):

Throughput Increase
Min = 2%
Max = 62%
Avg = 12%

Latency Decrease
Min = 7%
Max = 33%
Avg = 10%

Results of course depend of the SAN array used, and also on other factors.

Btw. this partition alignment should also be done in virtual machine (domU) virtual
disks. 

-- Pasi


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