Mailinglist Archive: opensuse (1468 mails)

< Previous Next >
Re: [opensuse] [OT] is there a virtual machine that IMPROVE performance by using harddisk as harddisk image
  • From: "Boyd Stephen Smith Jr." <bss@xxxxxxxxxxxxxxxxx>
  • Date: Tue, 2 Jun 2009 14:05:13 -0500
  • Message-id: <200906021405.13532.bss@xxxxxxxxxxxxxxxxx>
In <200906021759.42943.marix@xxxxxxxxx>, Matthias Bach wrote:
Am Dienstag 02 Juni 2009 17:57:46 schrieb Boyd Stephen Smith Jr.:
In <4A2547B0.8020706@xxxxxxxxx>, Sandy Drobic wrote:
The question itself is not relevant. Fact is that performance will
increase a lot if you use a raw device.

Well, then that software is written poorly.

No, but in the latter case every access will involve two filesystems and
an emulated block device instead of only one filesystem.

Not true. Once an mmap() or equivalent is done to the file data, the
filesystem basically gets out of the way. It has told the kernel where that
file is stored the (rest of the) kernel handles shuffling bits from RAM to
the disk, not the filesystem module.

Similarly, the loopback module gets out of the way once it has been
mmap()'d.

As I said, there is very little reason for a disk image to be slower than a
"raw" partition/disk. The evidence has already been presented; swap files
are nearly indistinguishable from swap partitions from a speed perspective,
even under heavy swapping.

That additional
overhead is something you will always see in io bound applications.

If the application is I/O bound it is, by definition, waiting on disk.
Therefore the additional RAM and CPU usage that might exist with going
through a filesystem module or block-device emulation will not slow it down.
--
Boyd Stephen Smith Jr. ,= ,-_-. =.
bss@xxxxxxxxxxxxxxxxx ((_/)o o(\_))
ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-'
http://iguanasuicide.net/ \_/

< Previous Next >