why partition filesystem size of filesystems allocate file systems space how big to make filesystems

From: mats@laplaza.org (Mats Wichmann)
Newsgroups: comp.os.linux.development.apps,comp.os.linux.misc,comp.os.linux.setup
Subject: Re: Why partition a perfectly good disk?
Date: Thu, 27 Sep 2001 16:46:33 GMT
Message-ID: <3bb354f8.11592188@news.laplaza.org> 
References: <v2lkqtgt231capetnmk1621qntkdmn7avk@4ax.com> 

On Thu, 20 Sep 2001 16:51:32 -0400, RJG <rjg@spam.net> wrote:

:I have noticed that many dedicated server hosting providers partition
:the disk as boot, usr, var, and home. Why?
:
:If the host BIOS won't recognize the full size of the disk, the boot
:partition is required for the kernel, but spreading the other
:directories across multiple partitions on the same drive just forces
:the drive to thrash more while eliminating any automatic optimizations
:that are built into the file system. Plus, it eliminates total
:flexibility by requiring that you decide ahead of time how much space
:to give each partition. 
:
:The only advantage to this scheme that I can see is it eliminates the
:possibility of users filling up the system partition and stalling the
:system, but there are better ways to accomplish this.
:
:Somebody, please explain the rational for this (as I see it) stupid
:partitioning scheme.


Many other answers.  Here's my take, roughly the way I present it in a
sysadmin class I teach:

Partitioning allows for: security (mounting key stuff read-only);
performance - parameterize different filesystems for different uses -
or even use different filesystem types; better alignment with backup
strategies; keeping filesystems small enough to fit on a tape; easier
upgrades - OS upgrades typically only affect system areas, user data,
if on a different partition can be left alone; and performance - I can
take two busy filesystems and put them on different disks, probably
making sure they're on the fastest part of the disk - performance is
better at the outer edge of the disk. I can also do things like mirror
key filesystems without having to go to the expense of mirroring
/everything/.

There are some downsides, too: mainly that if you didn't pick the
right sizes, it may bite you later, especially as OS upgrade time.
Logical volume management can be part of the solution to that,
potentially at a cost of performance, esp. if your carefully laid out
scheme now becomes non-optimal due to added space being on the same
spindle (longer seeks).  Actually, it seems to me that carving the
disk into pieces and asking LVM to combine those back into bigger
chunks is not the best way to handle it: why not give the whole disks
to the LVM system and let it handle the carving up within the LVM
layer, and then combine one or more of those pieces into filesystems.
I think only HP is doing that in a big way yet....


Mats Wichmann

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