Defrag issues

[Guest]

Hi-
I'm looking for any/all help on this. I am running Windows XP Pro on two
250GB Western Digital SataII drives, set up in a Raid0. Everything was great
until I recently tried to run defrag. I analyzed the volume and was told "you
should defrag this volume". I did, and it ran fine. After doing it, I
analyzed the drive once again and that I was once again told "you should
defrag this volume". The same case occurred even after a complete reboot.
Does anyone have any ideas what might be causing this? Any and all help is
greatly appreciated!

 

[Kyuzo]

Isn't Raid 0 striping without parity? Thats suppose to mean that you have
two hard drives hooked up to work in conjunction with each other. When you
save data, the data is divided to be equally stored on both hard drives.
Defragging a hard drive means to put data or files that fragmented
(scattered all over the place) back into one continuous link. Therefore, if
you are defragging a hard drive with Raid 0 setup, wouldn't you be losing
the benefit of the Raid setup?? The Raid setup is used to place less
overhead on a hard drive so they can last longer or perform better. Maybe
there could be third party defrag utilities out there to specifically handle
raid setups.

 

[Ken Blake, MVP]

Isn't Raid 0 striping without parity? Thats suppose to mean that you
have two hard drives hooked up to work in conjunction with each
other. When you save data, the data is divided to be equally stored
on both hard drives. Defragging a hard drive means to put data or
files that fragmented (scattered all over the place) back into one
continuous link. Therefore, if you are defragging a hard drive with
Raid 0 setup, wouldn't you be losing the benefit of the Raid setup??

No. See below.

The Raid setup is used to place less overhead on a hard drive so they
can last longer or perform better.

No. It has nothing to do with less overhead or lasting longer. Raid 0
(striping) is used to increase performance. It does that by writing
alternate pieces of the file to each of two (or more) drives. That makes the
writing (and subsequent reading) faster because you can do the I/O to the
second piece without having to wait for the first piece's I/O to finish (and
so on).

Regarding defragging, you're mixing up the way data is stored physically
with the way it's stored logically. Physically, the data is divided between
the drives, with alternates pieces going to alternate drives. But logically
the drives are treated as a single drive and defragging takes place in that
logical space.

So assume that you have two drives in a raid 0 array and there are 10 pieces
of a single file, and that the drive is unfragmented. It will look something
like this:

Drive 1 Drive 2
1 2
3 4
5 6
7 8
9 10

Then assume you add more data to the file. It gets fragmented and looks
something like this:

Drive 1 Drive 2
1 2
3 4
5 6
7 8
9 10

Data from another file............


11 12
13 14


The process of defragmenting will put this file into the following order:

Drive 1 Drive 2
1 2
3 4
5 6
7 8
9 10
11 12
13 14


It will *not* put all the pieces on either drive 1 or drive 2.

 

[Guest]

Ken-

Thanks for clarifying that for us, but that does not address the original
problem Do you have any insight?

Rick

 

[Ken Blake, MVP]

Ken-

Thanks for clarifying that for us, but that does not address the
original problem Do you have any insight?

Sorry, I don't remember the original question, but presumably I diidn't know
the answer, or I would have contributed to the thread earlier.

 

[Bob I]

The RAID drives appear to Windows as a single unit and so "defrag"
messes nothing up.

 

[Guest]

Ken-

Here is the original issue. Thanks for looking at this.

Rick
Hi-
I'm looking for any/all help on this. I am running Windows XP Pro on two
250GB Western Digital SataII drives, set up in a Raid0. Everything was great
until I recently tried to run defrag. I analyzed the volume and was told "you
should defrag this volume". I did, and it ran fine. After doing it, I
analyzed the drive once again and that I was once again told "you should
defrag this volume". The same case occurred even after a complete reboot.
Does anyone have any ideas what might be causing this? Any and all help is
greatly appreciated!

 

[Ken Blake, MVP]

Here is the original issue. Thanks for looking at this.

You're welcome, buit sorry, I can't help. I use a third-party defragger
(Perfect Disk), rather than the Windows one, and don't know a whole lot
about Windows defragger issues.

 

[Guest]

Hey Bob-

I get all that. My question is why, after I get a successful defrag, I
analyze the volume one more time and the tool tells me it still needs to be
defragged. Any ideas?

Rick

 

[Bob I]

What does the "report" say? It may be the "Analyze" feature is confused.
If you don't have a significant number of fragmented files, don't worry
about it. On the other hand if you have a significant number of OPEN
account files that are fragmented then login with a different account
and defrag.

 

[Kyuzo]

Thank for clearing that up for me. I know that it doesn't put all the file
pieces on one hard drive but I was just confuse because I thought by using
Raid 0, it would appear to the Defrag utitlity as having the hard drive
fragmented. Therefore, I thought it wouldn't benefit him much if he did do a
successful defrag because then it would hinder the raid array useless.

 

[Ken Blake, MVP]

Thank for clearing that up for me.

You're welcome. Glad to help.

I know that it doesn't put all the
file pieces on one hard drive but I was just confuse because I
thought by using Raid 0, it would appear to the Defrag utitlity as
having the hard drive fragmented.

The defrag utility, like other programs, doesn't even know there's raid 0 in
place it sees all of the pieces in their logical order, not the physical
one. That's the point of striping; how it works is hidden from applications.

 

[cquirke (MVP Windows shell/user)]

Thank for clearing that up for me. I know that it doesn't put all the file
pieces on one hard drive but I was just confuse because I thought by using
Raid 0, it would appear to the Defrag utitlity as having the hard drive
fragmented. Therefore, I thought it wouldn't benefit him much if he did do a
successful defrag because then it would hinder the raid array useless.

RAID operates at a far deeper level; both HDs will appear as a single
HD to the system, including defrag.

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