Date: Thu, 18 Oct 2001 16:35:07 -0400 From: Garance A Drosihn <drosih@rpi.edu> To: "David W. Chapman Jr." <dwcjr@inethouston.net>, "Rasputin" <rasputin@submonkey.net> Cc: "Doug Poland" <doug@polands.org>, <stable@FreeBSD.ORG> Subject: Re: dirpref gives massive performance boost Message-ID: <p05101000b7f4e90df4ca@[128.113.24.47]> In-Reply-To: <01c101c157f9$87868da0$fe0c4042@inethouston.net> References: <20010928141246.A15515@xor.obsecurity.org> <20011002212002.4034283f.steveo@eircom.net> <20011002214353.A653@student.uu.se> <20011018083713.A20403@polands.org> <20011018144850.A1943@shikima.mine.nu> <20011018105736.A43973@leviathan.inethouston.net> <p05101005b7f4bb89498e@[128.113.24.47]> <01c101c157f9$87868da0$fe0c4042@inethouston.net>
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At 12:22 PM -0500 10/18/01, David W. Chapman Jr. wrote:
> > Dirpref is not something which is "enabled" or "disabled", not in
>> the same sense as softupdates is "enabled".
>>
>> Dirpref is a smarter layout of information in a partition. You
>> need a version of the system which knows HOW to do that smarter
>> layout, and then you just rebuild the partition. There is no
> > switch to turn on and off.
>
>I'm not looking to turn if off or on, just to see whether a file
>system of mine has that capability in it or if I need to newfs it.
The point is that there isn't any single switch to look at to say
"ah, it is turned on". I suspect someone could write a program to
look at all the directory and file layout on your partition, and
based on that tell you that "74% of this filesystem has been build
using the newer, better rules for disk layout". The closer you get
to 100%, the better your performance is. The closer it is to 0%,
the more you have to gain by doing a backup+newfs+restore on that
partition.
> > Most easily done by temporarily adding an additional drive big
> > enough to hold all your stuff, and booting a fixit disk.
>
>Well yes, but I would like to avoid all of this if it is already
>using dirpref. I currently don't have enough drive space to fully
>backup my 24gig stripe set.
In some sense, there is an easy test for how much of your disk has
been built using the newer ("dirpref") layout. What operating
system are you running? (stable or current?) Let me assume "stable",
because I (personally) would not have the nerve to run that large of
a system on current... :-)
When was most of the information on that filesystem written? (I do
not mean "what is the last-datachg-time", I mean "when did the current
data get written to the current filesystem". For instance, if you
did a newfs on Sept 1st, and then did a 'tar xpf' of a huge archive
of older files, then the answer would be "Sept 1st", even though
many of those files (and maybe even directories) will have lastchg
times of some time in the past.
If most of the information on your disk was written before July 1st,
then chances are pretty good that about 0% of your disk has been
written using the newer, more optimal layout. If most of the info
was written on Oct 14th, then chances are that close to 100% of the
information is in the newer format. Again, there is no switch to
look at in the filesystem which will tell you that the filesystem
was build using the newer layout. It is just a question of whether
a given directory was created & filled up after the "dirprefs"
option was added to the system you are running. The higher the
percentage of directories which were written after that system
change, the closer you are to having "dirprefs turned on" for that
file system.
Unfortunately, I don't have a good idea of the exact date that your
system would have known to write information in the newer, more
optimal layout. So, this "easy test" isn't quite as useful as one
would want it...
--
Garance Alistair Drosehn = gad@eclipse.acs.rpi.edu
Senior Systems Programmer or gad@freebsd.org
Rensselaer Polytechnic Institute or drosih@rpi.edu
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