Reading from MSDOS and VFAT extremely slow (compared to ext2fs).

campbell@torque.net
Wed, 29 Oct 1997 07:50:48 +0000

I have found that both MSDOS and VFAT filesystems have very poor
performance when reading files (when compared to the write speed).
Linux kernels known to be affected include 2.0.29 and 2.1.60.

For example when using the "dd" command on the same HDD
(dd if=<src> of=<dest> count=81920)

Filesystem <src> <dest> Time (sec)
--------------------------------------------------
ext2fs /dev/zero xxxx 8.47
ext2fs xxxx /dev/null 9.80
vfat /dev/zero xxxx 7.72
vfat xxxx /dev/null 19.84

Note that "xxxx" is a local file (40Mb in size).

The harddrive is 1Gb IDE drive, similar statistics (ratio between
read/write times) are obtained for the parallel port ZIP drive. This
would indicate that the problem resides in the filesystem level.

This is of concern to me as I routinely recieve e-mail from various people
asking why the Linux driver is 3-4 times slower than the DOS driver. Till
now I have asked them to peform "dd" tests against the block device
(/dev/sda) which shows similar performance (often better) than the DOS
driver.

Does anyone have any idea what is causing the problem or suggest a fix?

David Campbell
=======================================================
campbell@torque.net (Parallel port device related mail)
dcampbel@p01.as17.honeywell.com.au (For all other mail)

Just when you thought you have seen every possible
parallel port chipset there is, some manufacturer comes
out with a new quirk. Just to make things worse, every
mainboard manufacturer on the planet decides to use it.