Compress and Defrag

T

TobyT

Hunter
I've never wanted to compress my data and with plenty of room on my harddrive, don't see the need. However, I do feel that defragmentation is a good idea. At present, I'm still using Diskeeper to defrag my Windows OS. Is this enough or does it even really work (the graphics show that it is, but . . )? Shouldn't there be some way to allow Parallels to defrag without compressing data?
LeslieT
 
Defrag Parallels files?

I never found the Windows defrag tool to be worth a thimble of spit. Diskeeper does a great job. But, that doesn't address the issue of defragging Parallels. We've had to uninstall and re-install various portions of Parallels in two separate instances. Does Snow Leopard defrag this automatically? If not, shouldn't there be a way for Parallels to clean up after itself WITHOUT compressing data?
Leslie
 
Maybe I misunderstand... what, exactly, is it that you want to defrag? If you want to defragment your VM's virtual hard disk, use (any) Windows defragging tool. If you want to defragment your Mac's (real) hard disk, use a Mac tool for that (although Apple says that defragging is no longer necessary now that hard disks have large onboard caches). But what exactly do you mean when you want to defrag Parallels (the software)?

Are you running your VM off Boot Camp or off a virtual hard disk?
 
Sorry I was unclear and thank you for replying. I'm running the VM off the virtual disk via Parallels. I am not using Boot Camp.

My concern revolves around the Parallels software. My first attempt to move my dying system over failed miserably when I could never get Parallels Tools 4 to install. Tech support took control of my computer via Mikogo and reinstalled Parallels (although he, too, had a terrible time trying to install Tools). So . . . it looks as if I have two vm machines on my computer. When I tried to delete the "old" non-functional one, I couldn't boot up the new, working one. So . . . I have two vms, but you can't open the "old" one.

I've kept the Windows os defragged (although now that I'm no longer using it for any internet usage, there's less to remove). After the four-hour marathon with India last weekend, I know a lot of junk was deposited on the hard drive. I've read that Apple keeps up with defragging. In posting, I'm trying to confirm that Apple is defragging Parallels on a regular basis. And that, other than Windows, I don't have to worry about extra files created by Parallels during/after technical support sessions.
Leslie
 
Hi Leslie,

Fragmentation is what happens to files when they get spread in pieces over your disk. Parallels, the software, doesn't need defragging - Software's just a bunch of instructions for the processor to do things.

The Mac's OS X is defragging files "on the fly", but only up to a certain size as far as I recall (there's an article in the Mac OS X knowledgebase about this, I'm sure you'll be able to Google it). Windows has its own on-board defragger, and as you mention there are 3rd party defraggers for Windows.

This is why I'm confused by your wanting to confirm that Apple is defragging Parallels - that just doesn't make sense; as regards fragmentation, Apple (the Mac OS) has nothing to do with Parallels (I guess you mean the Virtual Machine, or VM).

Now the virtual hard disk of your Virtual Machine is - to the Mac - just one big file that may very well be spread in pieces across your Mac's hard disk. Whatever is in that file, though, is visible (and defraggable) only to Windows.
You could have a Windows programm to defrag the files on the virtual hard drive, and then use a Mac program to defrag the "hard drive" itself (there are a very few Mac defraggers out there, none free) - this would ensure that your Mac's hard drive is fully defragged and, most importantly, your VM's hard drive is on the Mac's hard drive in one piece; and then your VM's hard drive would also be fully defragged.

However, as far as I understand, it's very unlikely that you'll see any substantial improvement in performance. OS's are quite good these days at dealing with fragmented files since most disks these days are fragmented anyway, and hard disk caches are big and fast enough to make fragmentation unnoticeable (or almost so).

In short - I wouldn't worry about fragmentation.

PS Defragmentation will - and should - absolutely not remove any files on your system. It should piece files together if they are on your drive in multiple fragments, but defragmentation should never delete any files or parts of them, regardless of whether they're useful or not. That's a job for different tools.
 
With 26 years of experience owning pcs, I understand what defragmentation does and why it was necessary with Windows. That's why I purchased a stand-alone program to keep my Windows hard drive defragmented. Naturally, I understand that everything is on the Mac's hard drive (I mean, where else would it be?). I keep the vm defragged on the Apple using Diskeeper. Of course, I know that Parallels is "separate" from the Apple OS.

I think we are at a dead end here. All I was trying to learn was: does Apple keep the Mac's hard drive defragmented after all the installing, uninstalling, and fiddling we've had to do with Parallels? Or, should I get a standalone program to do it?

I have no intention of using Parallels' Compression program. I don't want any of my data compressed. I didn't compress data in the past and am not interested in starting now, especially, now that we have such huge hard drives. I do believe in keeping programs and data defragmented.

I appreciate your trying to help, but believe we have a fundamental lack of understanding between us. Perhaps I was not as clear as I should have been.
Leslie
 
Yes, the Mac OS keeps the Mac's hard drive defragmented, up to a certain extent. This Apple support document has a little more information.
Parallels' disk compression works only on expanding disks. If you're using a fixed size VM disk it won't work. "Compression" here means "get rid of unused space, and shrink the VM hard disk file to save space on the Mac's disk". So no data will be getting compressed. Since I value speed more than space I converted my expanding disk to a fixed size one a long time ago.
 
Great answer

Shaddam, thank you so much. You've answered my question. Now that I understand what Parallels means by "Compress" I can run it. My problem was with Parallels' terminology. To me (and, probably, most previous Windows users) the term "compression" refers to reducing the size of specific files by means of an algorithm whereas the term "defragment" refers to reducing space on a given drive, but not in a specific file. If one had a pictorial display of a Windows OS drive, one would see little bits and pieces of files written in various locations, not necessarily together. The problem becomes exacerbated with uninstalls/re-installs until one has a real mess.

Since I began trying to get a description of what Parallels means by Compress, I've received several messages asking me to allow Parallels to "compress the vm." Now that I understand what the program means to do, I can permit it to be done. It would've been far easier for me to understand the manual, had the word defragment instead of compress been used. While data compression algorithms have probably improved, I remember when compressing individual files yielded inconsistent results, depending on the data in the individual file. I don't want to go there again! Hence, my questioning the terminology. From context, it had seemed to me that Parallels WAS talking about defragmentation, but its use of the term Compress confused me.

Thanks, again for keeping with this!
Leslie
 
> ... whereas the term "defragment" refers to reducing space on a given drive...

not quite so. I hope I'm not too pedantic with this ;.)... Defragmentation re-arranges the order of the individual pieces of files on a hard drive. Every file is being brokent down into pieces as it's written on the disk, that's the nature of how hard disks are formatted. Let's imagine your write a bunch of files to your disk. While you do that, file "MyDocument" is broken into pieces A,B,C as it's written to the disk. The file "MyPhoto" is broken down into "D,E,F,G", and "MySong" into "H,I,J,K,L,M". The sequence of pieces is A,B,C D,E,F,G H,I,J,K,L,M.

Now you erase "MyPhoto". The sequence is now: A,B,C, (Hole), H,I,J,K,L,M.

Next, you add the file "MyMovie"; it's broken into the pieces N,O,P,Q,R,S,T,U,V,W.

The beginning of this file neatly fits into the hole left by the former MyPhoto, and the sequence is: A,B,C N,O,P,Q H,I,J,K,L,M,R,S,T,U,V,W.

Defragmenting means that the system re-arranges the pieces to put the individual fragments of your files together in the proper sequence, so that - after defragmentation - the sequence reads A,B,C H,I,J,K,L,M N,O,P,Q,R,S,T,U,V,W.

So - no space is reduced or made free during defragging; only the pieces of files on your disk are re-arranged, which in old times made reading files into memory faster as the disk head didn't have to move all across the disk for the individual pieces. Also, there used to be programs that needed contiguous free space for operating properly, such as e.g. software that would record music or video - they don't need contiguous free space any longer since computers (and disks) have become so fast.

The point Apple is making is that with today's caching (and pre-fetching) technology built into hard drives and operating systems, having the bits and pieces of individual files all over the place on the disk doesn't matter - there's no significant performance hit. (I guess that's debatable if your disk is very full and very fragmented).

When Parallels say "Compress disk", they more than just invoke the (Windows) disk defragmentation: They actually erase the "free" bits from an expanding virtual disk file so that that file becomes smaller, thus saving space on the host's (the Mac's) hard dis. To get the free bits in one piece they first have to defrag the disk, otherwise the process would take ages (make a copy of the entire hard drive file, remove a tiny piece of free space from it, copy it again, remove another tiny piece etc.).

Again, I hope I'm not pushing it, I just wanted to make clear that defragmentation has nothing to do with freeing up space on a disk. It just makes it a bit easier and thus faster for the OS to fetch or write a file.

Cheers!
 
Hi Shaddam,

So I've read in a different thread that you should first defrag the host (Mac), then the guest, logic being, first get the VM file itself defragged, and then from within the guest OS defrag again. But you say the opposite. I see the logic in both, but what is the real answer?

Also, have you heard of V-locity from the Diskeeper folks? Is there a similar product for Parallels VMs?

Cheers!

PS - In reading the above thread, I admire your patience and generosity...
 
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