Should partition offset match stripe size?

Question

First of all I want to say, I am well aware of the misalignment that exists between block size and the parition offset. That's not what this is about.

My question is, should the partition offset be equal or a multiple of the stripe size. Currently we have RAID 1 meta luns with a 960K stripe on a DMX-4. We use a partition offset of 128 sectors (64KB). A Microsoft consultant beleives we should be using a parition offset of 1920 sectors (960KB).

All of the recommendations from EMC say to use 64KB, and it makes sense to me because 64KB is smaller than the stripe size. If it were larger then you could cross boundaries, but I don't want to dismiss this if it is important.

Has anyone ever done this or understand why this would be recommended?

Thanks!

Booyah2 · Accepted Answer

Hello NathanK,

I can see you have a expert handle on this topic, so the attached Engineering White Paper may just be useful to have around in case you need to explain this topic to your associate's in training. Just thought I would offer it up. Find Attached.

AranH1 · Answer

This is also the default now for Windows 2008, it will automatically create partitions with a 1MB alignment.

dynamox · Answer

new recomendation is to align by 1MB, see emc104675

NathanK1 · Answer

Ok, so there was a link from emc104675 to the following KB article: http://support.microsoft.com/kb/929491

If you look in the "More Information" section it describes a formula to use:

((Partition offset) * (Disk sector size)) / (Stripe unit size) = (any integer)

This seems to correlate with what the MS consultant was saying. It also seems to muddy what the powerlink article was stating.

In my scenario it would look like this:

1920 * 512 / 983040 = 1

I should be using the meta stripe size here shouldn't I?

Is this right or should I just stick with 1MB?

AranH1 · Answer

My understanding of that article is that the 1MB is a generaly safe recommendation to cover most array vendor strip sizes. All of the numbers you have tossed out though are all multiples of 64KB which was the offset Microsoft used to recommend before changing it to 1024KB, and is usually a multiple of an array stripe size. So I would say that any of those would be safe to use as they align on a 64KB boundary.

One thing though about your calculation, the article states that the forumula must all be in bytes or kilobytes, but you seem to have mixed sector count (1920) with bytes.

Symmetrix

Should partition offset match stripe size?

Was this post helpful?