Subject: Re: ufs filesystem tool: any interest?
To: der Mouse <mouse@Collatz.McRCIM.McGill.EDU>
From: Michael L. VanLoon -- <>
List: current-users
Date: 08/26/1995 22:02:56
>>> Actually, a more general tool which defragments and re-optimizes ufs
>>> filesystems might be more useful in that regard.

>> Have you (or someone else) actually measured the "fragmentation" of
>> real filesystems?

We did at Iowa State on the main servers (which served roughly 850
Unix workstations, with roughly 25,000 user accounts).

>Yeah.  As I understand it, the code is good enough that fragmentation
>is not a problem _if_ you allow it the 5%-10% free space it wants and
>keep turning files over, creating and removing them.

It's good in theory, but it doesn't work that way in practice with a
very busy file server.  The servers at Iowa State could get
significantly fragmented.  I believe they used a commercial
defragmenter on those machines (DEC Ultrix mostly) occasionally, and
the benefit was definitely a win.

I'm sure a full-feed USENET news server can also get hellishly
fragmented.  Maybe a heavily used database server?

>A defragger/reoptimizer would primarily be useful for filesystems (like
>/export/swap) which do not have the free space and constant turnover
>(ie, are very full and/or more or less frozen) and you want good
>performance out of.

On a "single user" workstation type system, I'm not sure the
fragmentation is serious enough to worry about.

  Michael L. VanLoon                       
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