Alan McKinnon wrote:
dd if=/dev/sda2 of=/dev/null
957169664 bytes (957 MB) copied, 17.5531 s, 54.5 MB/s
dd if=/dev/sda12 of=/dev/null
820854784 bytes (821 MB) copied, 21.4136 s, 38.3 MB/s
What do you conclude from this?
I'd say that /dev/sda2 is near "beginning" of disk (outer side,
more sectors per cylinder, higher transfer speed), and /dev/sda12
is near "end" of disk (inner side, less sectors per cylinder,
lower transfer speed).
Ah, I see my troll caught one already. You seem to be under the common
delusion that the structure reported by fdisk actually means something about
the physical disk :-)
Correct me if I'm wrong, but I do not remember saying anything like
that. And frankly, I can not image how you came to that conclusion.
I just said /dev/sda2 is probably on the outer side, and /dev/sda12
on inner side, based on that difference in transfer speeds...
These days the entire concept of a "cylinder" is a mere abstraction to make
tools like fdisk work in a sane manner.
Partially correct. True is, C/H/S numbers in fdisk does not have any
practical meaning these days. But there are still cylinders, heads
and sectors on disk. And total number of sectors reported by fdisk
is the same, as real total number of sectors on disk. These sectors
are numbered starting first with the most outer tracks on disk on
all physical cylinders, continuing towards the inner most track.
This holds true for nearly all sata/pata-disks. Maybe scsi/sas
have different sector numbering scheme...
But yes, it does seem that in this case sda2 is probably near the outer edge
of the platter where the head speed relative to the disk is higher.
Well, I'd say head speed does not anything to do with it. What makes
transfer rate on the outer tracks of disk faster is higher number of
sectors per cylinder, because nowadays disks have about constant
"bit-density" (only "about" constant, because number of sectors
per cylinder is a discrete number)...
Jarry
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