Date: Wed, 30 Aug 2000 15:57:10 +0930 From: Greg Lehey <grog@lemis.com> To: tony@aracnet.com Cc: questions@FreeBSD.ORG Subject: Re: Filesystem sizes for 4.x ? Message-ID: <20000830155709.A34589@wantadilla.lemis.com> In-Reply-To: <200008300611.XAA31925@shell1.aracnet.com>; from tony@aracnet.com on Tue, Aug 29, 2000 at 11:11:25PM -0700 References: <200008300611.XAA31925@shell1.aracnet.com>
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On Tuesday, 29 August 2000 at 23:11:25 -0700, tony@aracnet.com wrote:
>
> Can anyone give me the recommended filesystem sizes for FreeBSD 4.1 ?
>
> I've been upgrading from source since 2.0, upgrade to 3.x was painful
> as I ran out of space on / and /usr (had to start deleting unneeded binaries).
>
> Meant to repartition and rebuild 3.x but never got around to it, so will be
> dealing with this when I upgrade to 4.1.
>
> Couldn't find any mention of this in the release notes, FAQ, handbook or
> archives. If anyone knows where I could have found the info, short of
> trying a reinstall, LMK.
There are lots of different opinions about the correct size of file
systems. You're welcome to mine. Here's a repeat of something I sent
a couple of days ago.
Greg
What size partitions?
_____________________
In our example, we have 20 GB of space to divide up. How should we do it? You
don't have to worry about this issue, since sysinstall will do it for you if
you ask it, but we'll see below why this might not be the best choice. In this
section we'll consider how UNIX file systems have changed over the years, and
we'll look at the issues in file system layout nowadays.
When UNIX was young, disks were tiny. By the time of the Third Edition of
UNIX, in 1972, the system disk was a Digital RF-11, a fixed head disk with 512
kB. It was no longer possible to keep the entire system on this disk, so a
second file system became essential. It was mounted on a Digital RK03 with 2
MB of storage. To quote from a paper published in the Communications of the
ACM in July 1974:
In our installation, for example, the root directory resides on the
fixed-head disk, and the large disk drive, which contains user's files,
is mounted by the system initialization program...
As time went on, UNIX got bigger, but so did the disks. By the early 80s,
disks were large enough to put / and /usr on the same disk, and it would have
been possible to merge / and /usr, but they didn't. Since that time, an
additional file system, /var, has come into common use for frequently changed
data. This is what sysinstall does by default:
[Omitting PostScript image images/disk-label-default.ps 4i ]
Figure 6-12: Default disk partition sizes
It's relatively simple to estimate the size of the root file system, and
sysinstall's value of 50 MB is fine. But what about /var? 20 MB isn't worth
the trouble any more. In fact, both file systems put together would be lost in
the 19 GB of /usr file system. Why do we still do things this way? Let's look
at the advantages and disadvantages:
o If you write to a file system, a system crash can have serious consequences
for the data integrity of that file system.
o If you have a crash and lose the root file system, recovery can be difficult.
o If a file system fills up, it can cause lots of trouble. Most messages about
file systems on the FreeBSD-questions mailing list are complaining about file
systems filling up. If you have a large number of small file systems, the
chances are higher that one will fill up while space remains on another.
o In single-user mode, only the root file system is mounted. With the
classical layout, this means that the only programs you can run are those in
/bin and /sbin. In order to run any other programs, you must first mount the
file system on which they are located.
o It's nice to keep your personal files separate from the system files. That
way you can upgrade a system much more easily.
o It's very difficult to calculate the sizes of some file systems. For
example, on some systems /var can be very small, maybe only 2 or 3 MB. It's
hardly worth making a separate file system for that much data. On the other
hand, other systems, such as ftp or web servers, may have a /var system of 50
or 100 GB. How do you choose the correct size for your system?
o When doing backups, it's a good idea to be able to get a file system on a
single tape.
In the early days of UNIX, system crashes were relatively common, and the
damage they did to the file systems was relatively serious. Times have
changed, and nowadays file system damage is relatively seldom, particularly on
file systems that have little activity. On the other hand, disk drives have
grown beyond most peoples' wildest expectations. The first edition of this
book, only five years ago, showed how to install on a 200 MB drive. The
smallest disk drives in current production are 10 GB in size, more than will
fit on many tapes.
As a result of these considerations, I have changed my recommendations. In
earlier editions of this book, I recommended to put a small root file system
and a /usr file system on the first (or only) disk on the system. /var was to
be a symbolic link to /usr/var.
This is still a valid layout, but it has a couple of problems:
o In the example we're looking at, /usr is about 19 GB in size. Not many
people have backup devices which can write this much data on a single medium.
o Many people had difficulty with the symbolic link to /usr/var.
As a result, I now recommend:
o Make a single root file system of between 2 and 4 GB.
o Do not have separate /usr or /var file systems.
o Use the rest of the space on disk for a /home file system, as long as it's
possible to back it up on a single tape. Otherwise make multiple file
systems. /home is the normal directory for user files.
This layout allows for easy backup of the file systems, and it also allows for
easy upgrading to a new system version: you just need to replace the root file
system. It's not perfect, though: on a web server you probably wouldn't want
to put /var on the root file system.
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