Mike Christie wrote:
> Erez Zilber wrote:
>> On Tue, Feb 17, 2009 at 11:35 PM, Mike Christie <micha...@cs.wisc.edu> wrote:
>>> Erez Zilber wrote:
>>>> Hi,
>>>> I'm running a setup of open-iscsi connected to a target. When I run
>>>> I/O from the initiator (e.g using dd) with transaction size of 128kB,
>>>> I sometimes see that 2 128kB requests are aggregated to a single 256kB
>>>> request. This is rare, but it happens from time to time. Can I disable
>>>> this feature? Who is responsible for that? Is it scsi-ml?
>>> block layer.
>>> /sys/block/sdX/queue/max_sectors_kb
>> Thanks, but this will limit the I/O size for all I/Os. What I forgot
>> to mention is that sometimes I also send larger I/Os (e.g. 512kB).
>> With the proposed solution, these large I/Os will be sent as multiple
>> 128kB I/Os (and affect the performance). Isn't there a way to simply
>> avoid this aggregation?
> Not that I know of when going through the block layer. I think you will 
> have to ask lkml.
> I think the only way to control it is the  bsg/sg/passthrough route 
> since that does not do merging. The other alternative is to just hack 
> the code to do what you want :)

You can select the no-op I/O elevator and you can also use direct IO
like with sg_dd from the sg_utils package


You received this message because you are subscribed to the Google Groups 
"open-iscsi" group.
To post to this group, send email to open-iscsi@googlegroups.com
To unsubscribe from this group, send email to 
For more options, visit this group at http://groups.google.com/group/open-iscsi

Reply via email to