Re: disk or reiserfs problem?

[Oleg Drokin <green@namesys.com>]

Hello!

On Mon, Jun 02, 2003 at 01:00:36PM -0700, Jeff Breidenbach wrote:

> Incidentally, during the restoration I find that cp is 
> giving a throughput of about 1 MB/s when copying from 
> harddrive to harddrive. Both source and destination disks 
> use reiserfs and hdparm -tT reports about 50MB/s read rate. 
> Is a 1MB/s throughput expected when copying many small files?
> (There is a lot of data involved, so I probably have a couple 
> of days to ponder the question.)

Copying lots of small files can take lots of time just because you
cannot read those in order they are stored on disk platter. And you do not know
the order most probably. So the end result is the disk does constant seeking and
the speed is reduced. If you know the order in which files were written (e.g. alphabetically),
then you can read them in the same order (plain "cp -R . somedir" will read files in readdir order)
I am not very sure what can be done in such a case if you do not know the order in
which files were written. Perhaps if you copy the mounted backup drive to /dev/zero
(e.g. dd if=/dev/hdb1 /dev/zero bs=1024k count=500 (replace 500 with the half of your RAM
in megabytes) and you have large enough RAM, there is a chance that this will cache
enough data to keep stuff moving more quickly. 

Bye,
    Oleg