On Mar 11 2007 22:45, Ric Wheeler wrote:
> Jan Engelhardt wrote:
>> On Mar 11 2007 18:51, Ric Wheeler wrote:
>>
>> > During the recent IO/FS workshop, we spoke briefly about the
>> > coming change to a 4k sector size for disks on linux. If I
>> > recall correctly, the general feeling was that the impact was
>> > not significant since we already do most file system IO in 4k
>> > page sizes and should be fine as long as we partition drives
>> > correctly and avoid non-4k aligned partitions.
>> >
>>
>> Sorry about jumping right in, but what about an 'old-style'
>> partition table that relies on 512 as a unit?
>>
>>
> I think that the normal case would involve new drives which
> would need to be partitioned in 4k aligned partitions.
> Shouldn't that work regardless of the unit used in the
> partition table?
Assume this partition table on my current HD:
Disk /dev/hdc: 251.0 GB, 251000193024 bytes
255 heads, 63 sectors/track, 30515 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Start End Blocks Id System
/dev/hdc1 1 33 265041 82 Linux swap / Solaris
/dev/hdc2 34 30515 244846665 5 Extended
That is, 255 * 63 * 30515 * 512 == roughly 251 GB.
Now, if this disk was copied byte per byte (/bin/dd) to a
4096-based disk, and Linux would start using a sector size of
4096, then I would suddenly have
255 * 63 * 30515 * 4096 == 2 TB
Although I would not mind the 2 TB, the partition table would
read quite differently (note the Blocks column which is
multiplied by 4 (512x4=4096))
Device Start End Blocks Id System
/dev/hdc1 1 33 1060164 82 Linux swap / Solaris
/dev/hdc2 34 30515 979386660 5 Extended
Which would mean that the swap partition reaches into the real
data partition and would corrupt it.
That's what I am concerned about.
Jan
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