On Thu, 2 Dec 2010, Desai, Kashyap wrote: > > > > -----Original Message----- > > From: Kai Makisara [mailto:Kai.Makisara@xxxxxxxxxxx] ... > > You can't convert write of one block into multiple IOs. If someone > > wants > > to write 2 MB blocks, the system must transfer 2 MB in one IO. The > > choices > > are: > > I am not sure why single IO cannot be converted into multiple "IO" request. > If you run below commands > " sg_dd if=/dev/zero of=/dev/sdb bs=4800000 count=1" > > You will see multiple IOs(requests) are coming to low layer driver. > Yes, but each one is writing one or more disk blocks of 512 bytes. You don't see writes of partial blocks. If the block size of the device is 2 MB, the minimun IO request is 2 MB. (The SCSI commands for sequential access devices are different from the commands for block devices, but the minimum read/write unit is one block in both cases.) Kai P.S. Why is it necessary to use 2 MB blocks? Some people say that it is the optimal block size for some current tape drives. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
