Re: Is squeeze compatible woth WD20EARS and other 2TB drives?
Jochen Schulz put forth on 12/13/2010 3:51 PM:
> Mike Viau:
>>> On Mon, 13 Dec 2010 21:46:59 +0100 <ml@well-adjusted.de> wrote:
>>>
>>> Partition 1 does not start on physical sector boundary.
>>
>> I don't understand the implied meaning of this error? Did you take any
>> precautions as to the alignment of your partition? What about if you
>> were planning on having multiple partitions?
>From the linux-ide mailing list April 2010:
http://www.spinics.net/lists/linux-ide/msg37306.html
Unfortunately, sfdisk and cfdisk have no clue about alignment and
disks topology.
Now only the fdisk and parted commands are ready for new disks.
So the proper title of this thread should be:
"Does the Squeeze installer use fdisk or parted?"
As of April 2010, only fdisk and parted will create sector boundary
aligned partitions on drives that internally translate from 4K to 512B
sectors.
Linux typically reads 4K blocks. With a translated drive, two or more
512 byte sectors of a given block may lie on opposite sides of a
hardware 4K sector boundary. Thus, Linux will have to read two
consecutive hardware sectors instead of one in order to get the contents
of the 4K logical block. I.e. two reads (head seeks) per every 4k block
instead of one. Thus, you get half the performance vs a properly
aligned cylinder.
In the case of the WD20EARS this will drop your peak sequential read
rate from over 100 MB/s down to 50 MB/s or less. Without proper
alignment, you're literally leaving half of your drive's sequential read
performance on the table.
The story is even worse for 4K random writes. You'll drop your write
performance by a factor of 4 or more if you don't have proper alignment:
The moral of the story is, use fdisk or parted and make sure your
partitions are correctly aligned on 4KB boundaries. If the Squeeze
installer doesn't do so, I'd recommend booting an ISO or USB live distro
and partition the drive with fdisk or parted before booting the Squeeze
installer.
--
Stan
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