Gentoo Archives: gentoo-user

From: Alan McKinnon <alan.mckinnon@×××××.com>
To: gentoo-user@l.g.o
Subject: Re: [gentoo-user] Fragmentation of my drives. Curious mostly
Date: Sat, 29 Nov 2008 08:50:43
Message-Id: 200811291050.25525.alan.mckinnon@gmail.com
In Reply to: Re: [gentoo-user] Fragmentation of my drives. Curious mostly by Joshua Murphy
1 On Friday 28 November 2008 18:09:37 Joshua Murphy wrote:
2 > On Fri, Nov 28, 2008 at 6:46 AM, Alan McKinnon <alan.mckinnon@×××××.com>
3 wrote:
4 > > On Friday 28 November 2008 13:14:42 Dale wrote:
5 > >> If this is a little high, what would be the best way to defrag it?
6 > >
7 > > By not defragging it.
8 > >
9 > > It's not Windows. Windows boxes needs defragging not because
10 > > fragmentation is a huge problem in itself, but because windows
11 > > filesystems are a steaming mess of cr@p that do little right and most
12 > > things wrong. Defrag treats the symptom, not the cause :-)
13 > >
14 > > Reiser tends to self-balance itself out. What is especially noteworthy is
15 > > that none of the general purpose Linux filesystems provide a defrag
16 > > utility. Theodore 'Tso and Hans Reiser are both exceptional programmers,
17 > > if there was a need for such a tool they would assuredly have written
18 > > one. They did not, so there probably isn't.
19 > >
20 > > Any Linux defrag tool you encounter will have been written by a third
21 > > party separate from the developers. It will move blocks around and update
22 > > superblocks, the drive will have to be unmounted for that to work and a
23 > > slight misunderstanding of how to do it will ruin data.
24 > >
25 > > Are you willing to take the very real risk of data corruption?
26 > >
27 > >> Is
28 > >> there a best way? I do have a second hard drive that I back up too.
29 > >> Both Drives are 80Gbs and I do have a set of DVD back ups as well. I
30 > >> can update those pretty quick.
31 > >
32 > > --
33 > > alan dot mckinnon at gmail dot com
34 >
35 > While not trying to incite flames here... xfs isn't general purpose?
36 > xfs_fsr defrags xfs partitions while they're mounted and is designed
37 > to be used from cron (it's in xfsdump, not xfsprogs). File
38 > fragmentation, while a fact of life on any filesystem that sees any
39 > real use, does slow access times, as the drive head has to jump from
40 > one place to another, so a lot of fragmentation is a bad thing...
41
42 On a proper multi-user multitasking OS like Unixes, the heads are going to be
43 moving around all over the disk partition anyway just in general usage, even
44 with zero file fragmentation. How much extra movement does fragmentation
45 introduce?
46
47 I've been waiting for a proper statistical analysis of this question for
48 years. I'm still waiting :-) Besides, modern storage presents an extra
49 wrinkle. Defrag as most of the world knows it originated in DOS, where disk
50 sectors were guaranteed to be laid out on disk in the order of their sector
51 number. These days we have no such guarantee, and you cannot really be sure
52 if blocks are laid out contiguously on-disk just by looking at the blocks
53 numbers. I don't know of any filesystem tool that knows how to interrogate a
54 drive's firmware and get it right for every storage type out there.
55
56
57 > but
58 > as you say, we're not dealing with FAT based FS's here, so severe
59 > fragmentation only shows itself on very full filesystems. I very
60 > rarely see over 80% usage of my filesystems and have never
61 > consistently checked fragmentation levels, though, so I can't say
62 > whether xfs's being the exception on having a tool for the job means
63 > it particularly needed one...
64
65
66
67 --
68 alan dot mckinnon at gmail dot com

Replies

Subject Author
Re: [gentoo-user] Fragmentation of my drives. Curious mostly Dale <rdalek1967@×××××.com>