Re: tar: compress fast - extract very slow
- From: "Robert M. Riches Jr." <spamtrap42@xxxxxxxxxxx>
- Date: Mon, 22 Oct 2007 18:26:33 GMT
On 2007-10-22, shedir@xxxxxxxxx <shedir@xxxxxxxxx> wrote:
Hi folks,
I'm having this behavior on different machines and do not know why:
* I create a tar.gz-file VERY fast (about 20minutes for 120GB => 4GB
(=not much real data in it - mostly empty))
* I extract the same tar.gz-file BUT VERY SLOWLY (about 10 hours!!!)
At compressing the CPU-load is about 100% => OK
At extracting the CPU-load is about 25% => boring
Is this a problem of the filesystem or a problem of tar?
I have tried this on vmfs, ext3 and riserfs - always the same result!
How can I fix this - as I need a fast restore of the uncompressed file
in a disaster-event.
You list the compression size ratio as 120GB/4GB = 30. The
time ratio is 10hr/20min = 30. Hmmm...
when doing a full uncompress operation, it's writing the
120GB of data to disk. The writing of that much data would
appear to be disk-I/O-bound, which is why the CPU is only
25% busy. Being as you've tried different filesystem types
with no improvement, I would guess it's the physical disk
drive that's the limiting factor.
Have you tried simple ext2 rather than ext3? There's a
chance that _might_ help. Do you have DMA enabled on the
disks(s)? If not, that should help, provided it works.
--
Robert Riches
spamtrap42@xxxxxxxxxxx
(Yes, that is one of my email addresses.)
.
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- tar: compress fast - extract very slow
- From: shedir
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