Re: tune2fs -m "reserved space?"

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On 10/4/05, Arjan van de Ven <arjanv@xxxxxxxxxx> wrote:
On Tue, 2005-10-04 at 12:24 -0500, Justin Conover wrote:
> tune2fs
> -m reserved-blocks-percentage
> -r reserved-blocks-count
>
> If what I have read is correct, -m by default uses 5% of the disk
> space for "reserved root use"  On my server at home with a /home of
> 1TB thats about 50GB of wasted space.
>
> Is this reserved space actually used by ANYTHING?  Like LVM, some kind
> of fragmentation?

well for emergency root stuff; logging in without any disk space is
hard; lots of stuff wants to make temporary files etc.

but your second point it true too: most filesystems (ext3 but most
others) start to fragment like hell if they go over about 95% full.

Think of it this way: if you have half your disk empty, the filesystem
can do a proper job of finding non-fragmented space.
If only 0.0001% is free, it has almost no freedom of choice, resulting
in "you get it in whatever order some things become free".
Those are sort of extremes; there's been a bunch of research and the
outcome was that 5% free seems to be sort of the turning point in this
respect.

I suspect that research predates the Tb sized volumes, so I don't know
if it maybe is 1% on such volumes, but then again to some extend the
freedom needed will scale with the FS size


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This is a vg on the 1TB a 625GB slice, If i'm reading this correctly than I have about 32GB "free" space right?

vgdisplay "VolGroup01"
  --- Volume group ---
  VG Name               VolGroup01
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  5
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                2
  Open LV               2
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               931.53 GB
  PE Size               32.00 MB
  Total PE              29809
  Alloc PE / Size       20000 / 625.00 GB
  Free  PE / Size       9809 / 306.53 GB
  VG UUID               Lrid7V-3i0U-35SD-zLCU-kDYB-xmGu-r15Y6E

  df -k /dev/VolGroup01/LogVol00
Filesystem           1K-blocks      Used Available Use% Mounted on
-                       517924       184    517740   1% /dev


tune2fs -l /dev/VolGroup01/LogVol00
tune2fs 1.35 (28-Feb-2004)
Filesystem volume name:   <none>
Last mounted on:          <not available>
Filesystem UUID:          035dc33b-726e-40d0-8425-461f7b9b971b
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery sparse_super large_file
Default mount options:    (none)
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              65536000
Block count:              131072000
Reserved block count:     6553280
Free blocks:              33234208
Free inodes:              52339650
First block:              0
Block size:               4096
Fragment size:            4096
Reserved GDT blocks:      1017
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         16384
Inode blocks per group:   512
Filesystem created:       Sat Aug 27 07:34:52 2005
Last mount time:          Sat Aug 27 18:43:05 2005
Last write time:          Sat Sep 17 11:20:43 2005
Mount count:              9
Maximum mount count:      -1
Last checked:             Sat Aug 27 07:34:52 2005
Check interval:           0 (<none>)
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:               128
Journal inode:            8
Default directory hash:   tea
Directory Hash Seed:      8b7d8357-7489-4d3b-92da-8c186ecca90a
Journal backup:           inode blocks

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