Re: using direct IO with sgp_dd

[Douglas Gilbert <dougg@torque.net>]

Doron Shoham wrote:
> Bart Van Assche wrote:
>> On Tue, Mar 11, 2008 at 8:40 AM, Doron Shoham <dorons@voltaire.com> wrote:
>>>  sgp_dd if=/dev/sg1 of=/dev/null bs=512 bpt=128 thr=8 time=1 count=5M dio=1
>>>  time to transfer data was 2.236290 secs, 1200.36 MB/sec
>>>  5242880+0 records in
>>>  5242880+0 records out
>>>  Direct IO requested but incomplete 40960 times
>>>
>>>  What does it mean "Direct IO requested but incomplete 40960 times"?
>>>  And what could be the reason for this?
>> The man page of sgp_dd states that the parameter specified to bs must
>> be the block size of the physical device. You can query the block size
>> of a SCSI device with e.g. the scsi_readcap command:
>>
>> $ scsi_readcap /dev/sda
>> sg_readcap   /dev/sda
>> Read Capacity results:
>>    Last logical block address=625142447 (0x2542eaaf), Number of blocks=625142448
>>    Logical block length=512 bytes
>> Hence:
>>    Device size: 320072933376 bytes, 305245.3 MiB, 320.07 GB
>>
>> Bart.
> 
> Hi,
> sg_readcap /dev/sdb
> 
> Read Capacity results:
>    Last block address=3221225471 (0xbfffffff), Number of blocks=3221225472
>    Block size=512 bytes
> Hence:
>    Device size: 1649267441664 bytes, 1572864.0 MiB, 1649.27 GB
> 
> The block size is 512 as I used in the sgp_dd command.
> The problem is just when using dio=1, without it it works ok.

Doron,
Try reducing the bpt value (say to 64 or 32). To see more of
what might be the problem add 'verbose=<n>' to the command
line (and reduce the count to stop being flooded with
debug messages).

Doug Gilbert