Re: Defragging a directory?

[nathan@visi.com (Nathan Mates)]

In article <55upip$ic4@pith.uoregon.edu>,
Neil Parker <nparker@cie-2.uoregon.edu> wrote:
>In article <55ttr7$n5g@news.emi.com> drsmooth@relex.com writes:
>>I heard the UniDisk 3.5 goes at different speeds for accessing
>>different parts of the disk.  If so, it would be preferable to put the
>>subdirectory on a part of the disk that is spun at high speeds?

   [Actually, all 800K drives (well, maybe not the cheapo clones
Apple's now using) do the same speed slowdown.]

>I seriously doubt it.  Yes, the disk spins faster when the head is over
>the inner tracks, but the data are always tranferred at the same rate (0.5
>bits/usec) no matter how fast the disk is spinning.  So reading a directory
>block should take exactly the same amount of time no matter what track the
>block is on.

   Yeah, but there's also seek time. If the disk needs to spin to move
the sector into place, it's better that the disk is spinning faster--
on average, it'll find the right place. However, a defragged disk with
all of a subdirectory in a contiguous set of blocks can't be improved
by faster revolution since it's already in order.

   Then, there's also the right interleaving. Unidisks and the
interfaces can't handle data as quickly, so if the blocks are
interleaved any closer than 4:1, you'll have to spend a full
revolution waiting for a subsequent sector to be read. [Here again,
spin speed would have a slight effect].

   Appledisks can handle stuff at 2:1 before it'd start doing
pointless revolutions; 4:1 on an Appledisk means that it waits for 2
sectors to go by before it finds the right sector, but that's 2
sectors at the constant read speed.

   However, 3.5" disks in general are pretty dang slow after HDs.
Except for the very rare sneakernet or installing some stuff, I almost
never touch my stacks of 3.5" disks. [Especially true on my PC, where
pretty much everything is on CD-Rom nowadays; Ethernet (400-900K/sec
on an almost unloaded network) and Zip disks can handle any large
chunks of data I need to transfer.]

Nathan Mates

--
<*> Nathan Mates http://www.visi.com/~nathan/      <*>
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