alligning disks using diskpart..
Hi all, I was doing some research on storage for Exchange 2007 and - as with Exchange 2003 -came across articles refering to Diskpart for alligning partitions with the physical storage layout on disk. Most disks start of with the first track being 64 sectors (32kb using 512b per sector). Most articles therefore advise to allign the partition and start it off at the second track (after sector 64). Exchange would benefit from alligning the partition to an offset that is a multiple of 8192 bytes. This because it accesses the db in a 8kb random read/write. Some say that as much of every 8th read/write would need 2 I/O's based on the default misallignment of the partition, resulting in upto20% performance boost. I however did not see any significant improvements in the tests I performed. Also almost all modern disks use Zone Bit Recording which enables the vendors to have more sectors in outer tracks on a platter. So if each outertrack would contain more sectors, the allignment of the partition to the second track would in theory only be beneficial for pages on that second track and each track that has a exact multiple of16 sectors. Also, when keeping the partition disalligned other tracks would benefit in the same way. The outcome will be differentfor every hardware config you choose rigth?Sowhen do you allign the partition? There is no one-size-fits-all answer it seems. Am I mistaken? Ok... so I was searching for some more background info and real-life performance data, but was unable to find it. Can anyone direct me to some in-depth info on this subject or correct any errs I made in my analysis? Regards, Mark
October 17th, 2007 2:16pm

Exchange 2007 generated 75% less IO so going through the trouble of finding the answer to your question is only worth if you have thousands of users on your Exchange box Deli
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October 18th, 2007 11:26pm

Come on, being a technician yourself, don't you just want to know? So even if it would have minimal impact on user experience, it is still worth it.
October 19th, 2007 12:17pm

I found an article that might help you but as it appears it is vendor dependant Partition Alignment Most partitions are misaligned when created using the Disk Management tool and should be created with diskpart instead. Aligning partitions to track boundaries can have performance benefits, depending on the storage. Always use the storage vendor's recommended setting, but if your storage vendor does not have a recommended setting, use 64 sectors or 32KB. See the diskpar(t) blog for more details. http://msexchangeteam.com/archive/2007/01/15/432199.aspx Deli
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October 19th, 2007 12:32pm

Thanks, but I've already readmost ofthe common articles on storage for Exchange available on technet and the exchange blog. They are still to high level for what I would like to know. There are to many parameters involved to provide a one-size-fits all answer. Parameters like raid-level, disk type & geometry and the number of disks. Don't get me wrong, I always use the 64 sector allignment for new Exchange servers. It is just that Ihave neverseen any significant performance increase when jetstressing the database LUNS.This is what got me to start looking for more information. At first I contacted Hewlet Packard, because I mostly work with their hardware. They could not answer my questions. They even did not see the point in alligning the disks as there was no way of saying how the partitions (physically) set off whendisksare used in a RAID array. I was not satisfied with that answer, so that's why I started this thread, hoping a storage expert would read it and explain some more (or at least direct me to information) about the ins and outs of disk performance and how certain configurations would impact that.
October 19th, 2007 1:36pm

Maybe it is better to post a quest over at the Exchange Team blog? I do find it strange that even HP cannot answer that question! Deli
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October 19th, 2007 1:44pm

Most disks have something like 14 different zones containing a different number of sectors per track. You can only use diskpart to align the first zone. The remaining 13 zones will have a lower number of sectors per track. It seems to me that you could be aligned in the first zone and unaligned other zones, especially if they have an odd number of sectors per track. So, how can aligning the first zone do any good? This has puzzled me for years. Hats off to mpriem for your curiosity.
January 23rd, 2009 8:37pm

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