2009/1/7 Ralf Gross <Ralf-Lists AT ralfgross DOT de>:
> Sergio Belkin schrieb:
>> 2009/1/7 Ralf Gross <Ralf-Lists AT ralfgross DOT de>:
>> > T. Horsnell schrieb:
>> >> Ralf Gross wrote:
>> >> > Ferdinando Pasqualetti schrieb:
>> >> >> I think you should use /dev/random, not /dev/zero unless hardware
>> >> >> compression is disabled in order to have more realistic figures.
>> >> >
>> >> > This wouldn't be a good idea, /dev/random or /dev/urandom are just too
>> >> > slow in generating random data. To test the nativ speed of the  drive
>> >> > creating a file from /dev/urandom and writing this file then from
>> >> > tmpfs or a fast disk to the drive would be much better.
>> >> >
>> >> >
>> >> > Ralf
>> >>
>> >> Personally, I'd use /dev/zero with compression turned off.
>> >> Then there's *nothing* between the data-source and the tapedrive.
>> >
>> > Yes, but most people use hardware compresion with LTO drives. Sooner
>> > or later he has to test the drive with compression.
>> >
>
> Please always respond to the list...

OK, sorry, I am subscribed to many lists, I don't understand why it
not working reply...

>
>> Please look at the output, I've used urandom instead random, why so
>> poor performance?
>>
>> dd if=/dev/urandom of=/dev/nst0 bs=1M count=1000
>> 1000+0 records in
>> 1000+0 records out
>> 1048576000 bytes (1.0 GB) copied, 231.398 seconds, 4.5 MB/s
>
>
> It's what I wrote above. /dev/urandom is just too slow. You are
> measuring the speed of /dev/urandom not the drive.
>
> Try 'dd if=/dev/urandom of=/dev/zero bs=1M count=1000' and see what
> you get if you write to /dev/zero and not /dev/nst0. I bet it will be
> about the same speed because /dev/urandom is too slow for this.
>
> Ralf
>

You are right:

dd if=/dev/urandom of=/dev/zero bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 227.275 seconds, 4.6 MB/s


I want to tell you that I am not using software compression, and I
think as I posted earlier based on tapeinfo that tape drive is not
using hardware compression.

Why tape drive has such a poor performance?
-- 
--
Open Kairos http://www.openkairos.com
Watch More TV http://sebelk.blogspot.com
Sergio Belkin -

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