On 05/22/2010 05:46 PM, Les Mikesell wrote:
> Les Mikesell wrote:
>> Robert Nichols wrote:
>>> On 05/22/2010 11:29 AM, Les Mikesell wrote:
>>>> Robert Nichols wrote:
>>>>> On 05/21/2010 07:39 PM, Robert Nichols wrote:
>>>>>> You have another way out. By my calculation, that drive is partitioned
>>>>>> in DOS compatibility mode, which leaves the remainder of the MBR track
>>>>>> unused. Running fdisk in expert mode ("x" command), you can move the
>>>>>> partition's beginning of data ("b" command) from sector 63 back to
>>>>>> sector 56. That will give you the needed 4K alignment and a partition
>>>>>> that is no smaller than what it was before.
>>>>> Right idea, not the right procedure. You'll need to turn off DOS
>>>>> compatibility mode, then create the partition, and then go into
>>>>> expert mode and move the beginning of data from sector 1 to sector
>>>>> 56.
>>>>>
>>>> It ended up like this, but still sync'ing at about 4M/sec instead of 40.
>>>>
>>>>
>>>> Expert command (m for help): p
>>>>
>>>> Disk /dev/sdh: 255 heads, 63 sectors, 91201 cylinders
>>>>
>>>> Nr AF Hd Sec Cyl Hd Sec Cyl Start Size ID
>>>> 1 00 0 2 0 254 63 64 56 1465144009 fd
>>> Is that one of those WD drives that falsely reports its physical sector
>>> size as 512 bytes? I don't know if the kernel can always do the right
>>> thing when that happens, but all the reports I've seen say that getting
>>> the start of the partition aligned properly is sufficient.
>>>
>>> What does "hdparm -I /dev/sdh | grep 'Sector size'" show?
>>
>> It doesn't mention sector size. All of the size related options seem to match
>> the Seagate desktop drive.
>>
>
> 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.
--
Bob Nichols "NOSPAM" is really part of my email address.
Do NOT delete it.