On 05/22/2010 07:39 PM, Robert Nichols wrote:
On 05/22/2010 05:46 PM, Les Mikesell wrote:
Does the 4K sector size mean that the drive is going to read the 4K chunk then merge in the 512 bytes you wrote, the wait for the sector come around again to write it back? I guess that could explain the 10x write speed difference regardless of cylinder alignment. Read speed doesn't seem that much different.
Yes, that's exactly what it means. Every unaligned write or write that is not a multiple of the 4KB sector size becomes a read-modify-write within the drive, and a 10X reduction in write throughput is typical.
I should add that the kernel normally will do I/O in multiples of its 4KB (typical) page size where possible, but I have no idea whether any effort is made to align those writes if the drive does not report a 4KB physical sector size, or whether it even makes sense to try beyond what the elevator algorithm does for coalescing sequential writes.
I don't currently have any of these "enhanced format" drives, nor am I using RAID, so all I can report is the collected experience of others.