Fine sector adjustment on existing partition

  • Thread starter Thread starter rcebolleto
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rcebolleto

Ok, so I'm trying to optimize some servers that all have the 63 sector
(32256-byte) partition offset instead of the true 64 sector (32768-byte)
offset. Normally when I prep a server, particularly an Exchange of
VMWare (on windows) box, I use Diskpar to create my true 32k offset
partitions to minimize sector-boundary overlaps in the disk cache and
possibly on the actual writes.

However, I am working on some machines that have already been prepped -
OS loaded, all apps, all GPO's and AD and everything else. I'd rather
not format and redo the entire job if it can be avoided - I just want to
'nudge' the entire partition up one sector into alignment. However, all
of the partition tools I have played with (all the major ones like PM,
Acronis, Norton) deal in much, much larger chunks than a single sector -
they only adjust partitions several megabytes at a minimum. They clearly
are just designed for reorganizing space on a macro scale, not fixing
sector alignment issues.

I also tried getting clever about it and fooling with a hex editor and
dd (on a test drive, not on anything important) and *almost* got what I
wanted but I keep running into problems getting the bootloader to find
NTLDR or with NTFS not finding any files in the directory, or only some
of them, or worse. So before I dig into this again and kill another
weekend trying to figure out how to hand-craft the MBR, PBR, volume
extents and whatever else to make this work, I was wondering if anyone
heard of a tool that does this job?

THX!
 
Previously rcebolleto said:
Ok, so I'm trying to optimize some servers that all have the 63 sector
(32256-byte) partition offset instead of the true 64 sector (32768-byte)
offset. Normally when I prep a server, particularly an Exchange of
VMWare (on windows) box, I use Diskpar to create my true 32k offset
partitions to minimize sector-boundary overlaps in the disk cache and
possibly on the actual writes.
However, I am working on some machines that have already been prepped -
OS loaded, all apps, all GPO's and AD and everything else. I'd rather
not format and redo the entire job if it can be avoided - I just want to
'nudge' the entire partition up one sector into alignment. However, all
of the partition tools I have played with (all the major ones like PM,
Acronis, Norton) deal in much, much larger chunks than a single sector -
they only adjust partitions several megabytes at a minimum. They clearly
are just designed for reorganizing space on a macro scale, not fixing
sector alignment issues.
I also tried getting clever about it and fooling with a hex editor and
dd (on a test drive, not on anything important) and *almost* got what I
wanted but I keep running into problems getting the bootloader to find
NTLDR or with NTFS not finding any files in the directory, or only some
of them, or worse. So before I dig into this again and kill another
weekend trying to figure out how to hand-craft the MBR, PBR, volume
extents and whatever else to make this work, I was wondering if anyone
heard of a tool that does this job?

Quite frankly, I don't think what you are doing will result
in a measureble speed improvement. I think you are wasting
your time. Maybe you shpould first determine if your assumptions
are correct and then invest effort in doing this ''optimization''.

Arno
 
What do you think of this, then:

http://geekswithblogs.net/ntpro/archive/2005/08/11/49948.aspx

and this

http://lonesysadmin.net/2006/05/20/vmware-io-problems

and for some "official" treatment of the topic, this

http://www.vmware.com/pdf/esx3_partition_align.pdf

and a couple of whitepapers from HP on the same subject:

http://forums1.itrc.hp.com/service/...56062&admit=-682735245+1171130599425+28353475

I also have a Powerpoint from an EMC presentation on the same subject at
VMWorld 2005, which outlines the same issues and solutions (and points
out a flaw in DiskparT.exe as well, thus they recommend using Diskpar)

Actually, I agree it probably isn't going to make an enormous difference
but even if nothing else, it helps control for one variable when you're
trying to isolate other I/O performance problems, especially on a RAID.
 
Arno Wagner said:
Hmmm. Interesting.

That you were clueless again? No, not really.
This should not be happening. But apparently some systems are still
stuck in the dark ages and need this black-magic type optimizations to
perform well.

Ok, then. I take my statement back.

What statement. There was a statement?
Wasn't it just your usual rambling: "I have no clue but ramble anyway"?
 
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