COMPRESSING Drives

[WOOKZ]

does compression of the OS drive hamper proformance

 

[mosheen]

i'll say YES

 

[i789]

since you have to decompressing your OS when you use it, so I say you will take performance hit but depends on how much you compress it, the difference is going from small to a lot.

 

[newtekie1]

Definitely, not only does every file have to be decompressed before use, but the decompression and compression on every file access adds system overhead. The compression is smart enough to not compress the most commonly used OS files, but it still gives a pretty big hit on performance.

 

[[Ion]]

Yep, I had it set on my laptop because of the small disk (60GB), but it made things far slower, so now I just keep all of my junk on the 500GB disk in my desktop.

 

[RejZoR]

The hit is not all that high, even on lower end laptops. But it's there. Besides, with Windows Vista and above, you won't be able to compress system files when UAC is enabled. So, you'll be able to only compress data files.

 

[Deleted member 3]

Definitely, not only does every file have to be decompressed before use, but the decompression and compression on every file access adds system overhead. The compression is smart enough to not compress the most commonly used OS files, but it still gives a pretty big hit on performance.

Pretty big hit? Happen to have some numbers on that?

From what I know there are even some cases where NTFS compression improves performance, can't find a decent article atm though. I haven't run any benchmarks on compressed drives in ages, though one of the drives in my server is compressed and I don't notice any performance issues (perhaps it's a few % lower, but certainly not a "pretty big hit"). I'm guessing performance increases basically can happen when compression is high enough to reduce disk access enough to matter (ie 50% compression > 50% less reading from disk) and CPU's being able to decompress faster than it would take the disk to read that other 50%. Though I can't back that up with any actual facts.

 

[Deleted member 3]

It's the legacy disk, thus no RAID applies (for those who think it's some array). The controller doesn't have on board cache either that affects anything.

A bit hard to read due to the cached read, but the write speeds seem fine, even though you can't read it very precise.

 

[Mussels]

when you use file compression, in order to read them they have to get uncompressed into system memory, and written temporarily back on the HDD.


its not an optimal solution at all.


XP/vista/etc already compress some files, mostly system restore/SP uninstall folders and such.

 

[W1zzard]

there is a break even point, when the drive takes longer to read the data than the cpu needs to compress/decompress it and you have that amount of cpu power idle anyway

 

[Deleted member 3]

and written temporarily back on the HDD.

Why? Source?

 

[Mussels]

Why? Source?

i remember it from a course i took, which made me go and format my HDD's to a 64K cluster size... which then made XP impossible to install due to service pack 2 cracking the shits about not being able to compress its uninstaller.

its half related, but its WHY i remember it.


will google for details now


ding, found it


http://support.microsoft.com/kb/307987

You may notice a decrease in performance when you work with NTFS-compressed files. When you open a compressed file, Windows automatically decompresses it for you, and when you close the file, Windows compresses it again. This process may decrease your computer performance.

underline my emphasis



more
http://support.microsoft.com/kb/251186/EN-US/

NTFS compression has the following performance characteristics. When you copy or move a compressed NTFS file to a different folder, NTFS decompresses the file, copies or moves the file to the new location, and then recompresses the file. This behavior occurs even when the file is copied or moved between folders on the same computer.

it may be me interpreting it wrong, but it clearly sounds like its decompressing it to a file and not leaving it in memory

 

[W1zzard]

it [ntfs compression] decompresses to memory

it's not even half related .. it's 0 related .. well it uses the same word, but that's it

 

[Deleted member 3]

i remember it from a course i took, which made me go and format my HDD's to a 64K cluster size... which then made XP impossible to install due to service pack 2 cracking the shits about not being able to compress its uninstaller.

its half related, but its WHY i remember it.


will google for details now

The installer doesn't work on file system level though.

 

[Deleted member 3]

it decompresses to memory

And I doubt it will decompress the whole file first, I'm guessing it decompresses the stream of data on the fly, similar to network compression. I can try with some large iso, gimme a min.

 

[Mussels]

The installer doesn't work on file system level though.

i'd install XP, it'd go well, then it'd BSOD on boot.

ok w1zz, so its 0.00001% related - like i said, its just WHY i remembered it.

 

[W1zzard]

http://www.sandersonforensics.com/Files/NTFS compression white paper.pdf

read that before making any bold claims

 

[Mussels]

weee, a PDF!


its not like i'm going to disagree with evidence here, i was merely stating what i had been taught (and until now, beleived due to lack of contrary evidence)


edit: i read that, and dont see it mentioned specifically whether or not decompressed files are left in ram, or decompressed to the drive.


edit 2: thinking about it, what i learned may have been the compression used on fat32 drives (if there was one?) it was around the early XP days when i did this course.

 

[Deleted member 3]

weee, a PDF!


its not like i'm going to disagree with evidence here, i was merely stating what i had been taught (and until now, beleived due to lack of contrary evidence)


edit: i read that, and dont see it mentioned specifically whether or not decompressed files are left in ram, or decompressed to the drive.


edit 2: thinking about it, what i learned may have been the compression used on fat32 drives (if there was one?) it was around the early XP days when i did this course.

FAT32 doesn't have compression, you're probably speaking of things like drivespace/doublespace/norton speeddisk/etc. Those do not work on file system level.


I just formatted a 128MB USB stick as NTFS and enabled compression. I wrote a 56MB file to it twice. So ther eis no space to decompress anything. When I double click either file it instantly opens, so it's not decompressing the whole file, just the stream of data. Also, it's not storing any of this to the stick. You could argue it's storing elsewhere, I doubt that. Test that yourself by using a single drive for the OS and filling it completely. I'm pretty sure the system won't crash because it can't read files.

 

[Mussels]

good test dan, ah well.
my guess would be that if it WAS storing it somewhere, it would be on the C:\ drive in a temp folder - perhaps test with a large file, open it, and then see if your free space lowers?

i need to get proven wrong on something at least once a month, or my ego gets too big

 

[Deleted member 3]

good test dan, ah well.
my guess would be that if it WAS storing it somewhere, it would be on the C:\ drive in a temp folder - perhaps test with a large file, open it, and then see if your free space lowers?

i need to get proven wrong on something at least once a month, or my ego gets too big

It's file system level compression, why would it use Windows directories? I doubt the file system actually asks Windows where to store files.

I think it's best to compare to playing porn on your computer. You select the middle of the movie (the part where they lez it out), the system reads only that part of the movie and decompresses those frames on the fly. It does not decompress the whole movie on the disk before it can play anything, it does not require temporary files of any kind. It's instant access to compressed data without fancy requirements. And sure there probably is some small buffer in the memory, but I doubt it's large enough for you to notice it.

 

[Mussels]

hahhaha, porn references. awesome.


(i'm not arguing with you on this, merely getting as much information as i can)