[H-GEN] partition advice

[Martin Pool]

davidj at amh.com.au wrote:

> The primary FAT, or primary superblock is in the center of the drive, and
> using some form of tree, get to anywhere in the disk in minimum _average_
> time. 

> The theory behind this is the disk heads are on average, located
> in the center of the platters.

Is that really true?  It sounds a little statistically suspect to me.  I
seem to remember that the current-best seek algorithms spread the
head-presence-probability evenly over the disk.

Of course, the heads _will_ tend to be located over busy partitions, so
perhaps it's better to locate your busy partitions next to each other...
and I suppose it's easier to pack them together in the centre.

But which partitions will be busiest?  That's not necessarily
straightforward, because caching plays such a major role in modern
systems.  Even though the root is the "most important", it's possible
that the head actually isn't there very much of the time: the
directories (/, /bin, /etc) are extremely likely to be in cache, as are
many of the relatively small files found on that partition.  Conversely,
/var and /home are likely to contain many infrequently-accessed files,
and so suffer more physical I/O.  

If your machine swaps a lot, then the swapspace should be in the
high-traffic area.  If (like wistful) the machine rarely uses swap,
there's not much point giving it premium real-estate anyhow.

There's probably some kind of similar analysis on choosing the right
group sizes under ext2fs.

It might be worth looking at how many actual physical I/Os happen on
various partitions.

-- 
 /\\\  Mincom | Martin Pool          | martin.pool at mincom.com
// \\\        | Software Engineer    | Phone: +61 7 3303-3333
\\ ///        | Mincom Pty. Ltd.     | 
 \///         | Teneriffe, Brisbane  | Speaking for myself only

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