Help understanding HDD Offset

[Tripredacus]

I am reading through a new Best Practices document that was delivered to me, and it speaks of using Diskpart to specify an offset for greater disk performance. The problem is, I am not understanding how to determine this information. Offset is a var that can be used in the Diskpart.exe cmdline. Here is some more info:

The byte offset at which to create the partition. If no offset is given, the partition will start at the beginning of the first free space on the disk. For master boot record (MBR) disks, the offset is cylinder snapped; the offset is rounded to the closest cylinder boundary. For example, if you specify an offset that is 27 MB and the cylinder size is 8 MB, the offset is rounded to the 24 MB boundary.

Currently, we do not specify an offset. What do I need to do in order to determine which offset to use? I understand its function and see the example, I just can't find any information about how to figure it out.

[jaclaz]

Simple math?

You can use this small spreadsheet, though it was intended for another use, it can serve your purpose:

http://www.boot-land.net/forums/?showtopic=2959

(hint: offset should be the value "sectors before")

or are you asking about which values are appropriate to better performance?

I know nothing of this latter aspect, unless you are referring to this:

http://support.microsoft.com/kb/929491/en-us

If the document is not proprietary/reserved, can I have a look at it?

jaclaz

Edited March 12, 2009 by jaclaz

[James_A]

Presumably this only applies to legacy Operating Systems?

AFAIK the whole idea of aligning with cylinder boundaries was abandoned a couple of years ago, when Vista arrived.

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[submix8c]

May be true (no clue on that), but the OP refers to "best practices" and "greater disk performance" which still applies ("beating up the Physical R/W head"). Even in the "Olden Days" of IBM Large Mainframe Disks the practice was to put the "index" in the Center Of The Disk on Physical Cylinder Boundaries and the most-often-used files Nearest the Index on Physical Cylinder Boundaries, thereby reducing Seek Time, etc etc.

[Tripredacus]

or are you asking about which values are appropriate to better performance?

I know nothing of this latter aspect, unless you are referring to this:

http://support.microsoft.com/kb/929491/en-us

If the document is not proprietary/reserved, can I have a look at it?

jaclaz

I'll take a look at that spreadsheet in a little bit. As far as the article, I've seen things like that also, that specify the /align flag, but the document refers to setting the /offset tag.

The document falls under NDA (Non-Disclose Agreement) Rules, and is in Beta/Draft stage. This is the rules from Microsoft, not from my company. They provided this doc to us. I cannot post anything about it, not even the name. Sorry.

Presumably this only applies to legacy Operating Systems?

AFAIK the whole idea of aligning with cylinder boundaries was abandoned a couple of years ago, when Vista arrived.

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The document speaks directly regarding Windows 7, Vista SP2 and 2008 SP1. An idea that the image should be applied to the outmost part of the disk as possible, as that is where data starts to be read. This is comparative to how a record (LP) works, as opposed to how a CD or DVD is read, which is from the inside out.

[submix8c]

Oho! Sounds like this has something to do with Images for an install? If so, makes sense (even though the CHR-concept as applied to LBA applies, not "continuous" per-se).

Kind of like "put it to the outside, where it won't be used that often; we'll put the oft-use in front of that".

Ok, outside of my scope of knowledge (the image part), so I'm outa here!

Good luck, and HTH!

[jaclaz]

Yep, but still you are failing (and this is surely not under a NDA ) whether you want a tool to be able to calculate exactly an offset (which the spreadsheet might be) or if you want to know a suggested range (for which anything in this thread is pretty much useless).

The Server 2003 diskpart.exe has the same (though with another "unit of measure") function of diskpar:

http://www.messagingtalk.org/content/69.html

http://msexchangeteam.com/archive/2005/08/10/408950.aspx

I cannot see any difference between "offset" and "align", unless this one (maybe):

http://nathanbean.com/wp/?p=13

This should be the (hopefully complete) diskpart commands explanation, though it is not really clear:

http://technet.microsoft.com/en-us/library/cc766465.aspx

jaclaz

[James_A]

Even in the "Olden Days" of IBM Large Mainframe Disks the practice was to put the "index" in the Center Of The Disk on Physical Cylinder Boundaries and the most-often-used files Nearest the Index on Physical Cylinder Boundaries, thereby reducing Seek Time, etc etc.

Hey, I remember those - we had disk drive housings the size of washing machines and removable disk platters the size of car tyres on the ICL and DEC System 10 mainframes.

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