In <200906021759.42943.marix@marix.org>, Matthias Bach wrote:
Am Dienstag 02 Juni 2009 17:57:46 schrieb Boyd Stephen Smith Jr.:
In <4A2547B0.8020706@drobic.de>, 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@iguanasuicide.net ((_/)o o(_)) ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-' http://iguanasuicide.net/ _/