On 5/27/2010 10:33 AM, sensille wrote:
(resent because of received bounce)
Edward Ned Harvey wrote:
From: sensille [mailto:sensi...@gmx.net]
So this brings me back to the question I indirectly asked in the
middle of a
much longer previous email -
Is there some way, in software, to detect the current position of the
head?
If not, then I only see two possibilities:
Either you have some previous knowledge (or assumptions) about the drive
geometry, rotation speed, and wall clock time passed since the last
write
completed, and use this (possibly vague or inaccurate) info to make your
best guess what available blocks are accessible with minimum latency
next
...
That is my approach currently, and it works quite well. I obtain the
prior
knowledge through a special measuring process run before first using the
disk. To keep the driver in sync with the disk during idle times it
issues
dummy ops in regular intervals, say 20 per second.
or else some sort of new hardware behavior would be necessary.
Possibly a
"special" type of drive, which always assumes a command to write to a
magical block number actually means "write to the next available"
block or
something like that ... or reading from a magical block actually
tells you
the position of the head or something like that...
That would be nice. But what would be much nicer is a drive with an
extremely
small setup time. Current drives need the command 0.4-0.7ms in advance,
depending on manufacturer and drive type.
Technology like DDRdrive X1 (which is well beyond $200) doesn't have
this problem. The setup times for that kind of hardware are measured in
usec. (I.e. measured in PCI cycles.)
- Garrett
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