Re: disk or reiserfs problem?

[Hans Reiser <reiser@namesys.com>]

Oleg Drokin wrote:

>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
>
>
>  
>
Your performance will improve after the restoration though....

-- 
Hans