Re: SCSI tape access on 2.6 kernels?

Chip Coldwell
2006-01-24T20:59:11Z

On Tue, 24 Jan 2006, Kai Makisara wrote:
>>
>> Put
>>
>> options st try_direct_io=0
>>
>> in /etc/modprobe.conf. Direct I/O defeats read-ahead, and
>> significantly (factor of >5) degrates read performance. I don't know
>> about writes.
>>
> The only thing that could be seen in Gerhard's tests with try_direct_io=0
> should be higher CPU load. It probably won't have any effect on the speed
> in these tests.

I will let Gerhard speak for himself, but it made an enormous
difference in our tests. The buffer size in the tape device is 64K,
matching the read-ahead to that buffer size gave maximum performance.

Chip

--
Charles M. "Chip" Coldwell
Senior Software Engineer
Red Hat, Inc