i’m in position now talking between DBA’s and SAN admins about the 128K small stripe size. Do you know if metadata is in the declared strip sizes or if it outside of it? If it is outside of it, how much metadata is there per a given extent size (128K in this example)?

You’d probably benefit from reading the Oracle Press book on ASM written by Murali, Nitin, and Rich. I’ve just about finished it and found it an excellent resource for technical information. It covers extent allocation, striping, and more with a good amount of detail. It also does a great job of easing into those deep details, so it’s also well-suited for those new to ASM. At about 280 pages, it’s also a pretty quick read (I am a slow reader, so that’s important to me), so you could probably knock it out in a few days.

The coarse-grained stripe size is always equal to the AU size.

The course-grained stripe size is the extent size. The 11g manuals seem to refer to both a DISKGROUP AU (au_size property) and a FILE AU (extent). The metalink article you quoted seems to fit with this terminology too.

It’s a mess; I hope they clean it up in 11g release 2 (whenever that actually gets released).

I agree it is confusing. But I think it might have to do with the behavior in 10g where extent and AU are always the same size thus two words are used interchangeably. However, this is “not” always true in 11g.


allocation unit = extent size
40000>extent>20000 => FILE_AU=DISKGROUP_AU*8.

I assume you meant -

Number of extents  Extent Size
<20,000           AU
≥20,000 and <40,000  AU * 8
≥40,000          AU * 64

[reference]

So the “FILE_AU” is actually the “extent”, and “DISKGROUP_AU” is the “AU” we always refer to.

Based on the statement in metalink note 465039.1 shown below, above statement makes sense.

“Also, note that in ASM the space is managed logically using Allocation Units (AU) at the disk level and Extents at the file level”

“Suppose you have a diskgroup with 1MB AU size. After a particular file has 20000 extents, the allocation unit for that file becomes 8MB.”

When first read this, my first impression was “after 2000 extents, the AU (implying DISKGROUP_AU) becomes 8MB in size”, which I don’t think that is the case. After 20000 extents, the extend size will become 8MB because the extent size is now 8 times of the AU size. The AU size still remains at 1MB. The word “allocation unit for that file” threw me off. However, if I replace it with FILE_AU (which is extent), it makes more sense. Is this what it meant here?

Great investigation.

Thanks,

Ittichai