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jim33boy
Enthusiast
Enthusiast

Proper alignment for 320k chunk size

Hello,

I know that by default Windows 2003 aligns partitions with an improper staring offset, usually 63.. I have read multiple links on the web stating to use create partition primary align=64..

My VDISK that I am curerently working with has a 320k Chunk size so i am not sure align=64 is the correct setting here because of this link..

http://support.microsoft.com/kb/929491

It states for a 256k chunk size the proper setting for the offset is 512 as seen below.

To verify that an existing partition is aligned, divide the size of the stripe unit by the starting offset of the RAID disk group. Use the following syntax:

((Partition offset) * (Disk sector size)) / (Stripe unit size)

Note Disk sector size and stripe unit size must be in bytes or in kilobytes (KB).


Example of alignment calculations in bytes for a 256-KB stripe unit size:

(63 * 512) / 262144 = 0.123046875
(64 * 512) / 262144 = 0.125
(128 * 512) / 262144 = 0.25
(256 * 512) / 262144 = 0.5
(512 * 512) / 262144 = 1

Example of alignment calculations in kilobytes for a 256-KB stripe unit size:

(63 * .5) / 256 = 0.123046875
(64 * .5) / 256 = 0.125
(128 * .5) / 256 = 0.25
(256 * .5) / 256 = 0.5
(512 * .5) / 256 = 1

These examples shows that the partition is not aligned correctly for a 256-KB stripe unit size until the partition is created by using an offset of 512 sectors (512 bytes per sector).

Now since my chunk size is 320k, I am thinking I should use 640 as the offset as seen here..

(640 * 512) / (1024*320) = 1

So I am not sure if I should go with the generic "create partition primary align=64"

Or

With the 640 alignment "create partition primary align=640"

Does anyone know the correct answer here? Will either or work?

Thanks

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jim33boy
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Anyone, anyone..Bueller, Bueller.

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mcowger
Immortal
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Why do you think you have a 320byte block size?  That would be extremely uncommon, and no matter what offset you chose, you'd end up with unaligned IOs to your disks...

--Matt VCDX #52 blog.cowger.us
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jim33boy
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Hi MCowger,

Well I think I have a 320k chunk size because that's what the Vdisk says it is set to. I have attached two pictures to clarify...Pic 1 shows the chunk size and Pic 2 shows the 5 RAID sets.

The thing is that this is RAID 50.. There are 5 RAID5 sets.. If each of these RAID5 sets was 64k Chunk size then 320k would be the aggregate chunk size for the 5 RAID 5 sets..

So 64 x 5 = 320

But I am not sure if that's how it works with RAID 50. Theoretically if one chunk only lives on 1 RAID5 set and that chunk for that RAID5 set was set to 64k I would be OK.. Again I am not sure how RAID 50 works.. I inherited this setup.

Thanks and please advise..you are the only hit I got..  I have asked HP if they know how the Chunk size lays out for RAID 50 but nothing back yet.

Thanks again

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