Scot Jenkins wrote:
> Anyone running LVM and have comments about the amount of overhead it
> uses? Here's my setup:
>
> Debian woody 2.4.27 kernel w/LVM compiled in. Box his attached to a
> jetstor filer that hands out a chunk of disks as a single scsi target.
> The jetstor is doing RAID-5. I know little else about the filer,
> someone else admins' it.
>
> dmesg shows:
> SCSI device sda: 627932160 512-byte hdwr sectors (321501 MB)
>
> If is just run fdisk, create one partition and then run
> "mke2fs -j -m1 /dev/sda1" I get:
>
> Filesystem 1k-blocks Used Available Use% Mounted on
> /dev/sda1 309030804 32828 305858396 1% /jetstor
>
>
> If I setup the disk via LVM (pvcreate, vgcreate, lvcreate) I get:
>
> Filesystem 1k-blocks Used Available Use% Mounted on
> /dev/vg01/lv00 263191620 32828 260484924 1% /jetstor
>
> I get the same results whether I use the entire disk "/dev/sda" or
> create a single partition of type "Linux LVM" (8e).
>
> Any idea why LVM takes about 45 GB of overhead?
Answering my own post: man vgcreate
-s, --physicalextentsize PhysicalExtentSize[kKmMgGtT]
Sets the physical extent size on physical volumes
of this volume group. A size suffix (k for kilo-
bytes up to t for terabytes) is optional, megabytes
is the default if no suffix is present. Values can
be from 8 KB to 16 GB in powers of 2. The default
of 4 MB causes maximum LV sizes of ~256GB because
as many as ~64k extents are supported per LV. In
case larger maximum LV sizes are needed (later),
you need to set the PE size to a larger value as
well. Later changes of the PE size in an existing
VG are not supported.
Note where it says "The default of 4 MB causes maximum LV sizes of
~256GB ". By using the "-s" option to increase the physicalextentsize
in the volume group, I was able to create about a 300 GB logical volume:
# vgcreate -s 32M vg01 /dev/sda
Tip: run "vgdisplay -v" after you run vgcreate and pay attention to the
"MAX LV Size" value.
# vgdisplay -v /dev/vg01
--- Volume group ---
VG Name vg01
VG Access read/write
VG Status available/resizable
VG # 0
MAX LV 256
Cur LV 1
Open LV 0
MAX LV Size 2 TB <===== NOTE now 2 TB, not 255 GB (default)
Max PV 256
Cur PV 1
Act PV 1
VG Size 299.38 GB
PE Size 32 MB
Total PE 9580
Alloc PE / Size 9568 / 299 GB
Free PE / Size 12 / 384 MB
VG UUID cf1kZt-pIVd-THrj-dovU-00Id-KY36-AvGTUJ
--
scot
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