max number of PE per PV

[Jdamian]

I created a VG on 54 pvs whose size is near 7.3GB (OPEN-9 in a XP).
I wanted to set a value of "max number of PE per PV" according to the vgcreate man pages.

I tried to use "-e 2048" but the vgcreate command failed: "Too large file"

I tried a lot of values until I got 1788.

First, I believed that was a max value accepted by vgcreate but the VG00 in the same system has got a value set to 2000.

Why cannot set a desired value ?

P.D: I want to set a bigger value because I may need later to add PVs greater than 7.3 GB.

Thanx in advance

[eran maor]

Hi

the reson that you cant do more then 1788 pe is becuase the size of pe is 4 m.b and 4 * 1788
is 7.2 g.b .

my advise is to work with less pe size if you want to work with more pe in this vg .with the option -s for pe size check it in the man pages

[Printaporn_1]

increase PE size from 4 to 8 will help

[Stefan Farrelly · Accepted solution]

You need to increase the PE size to compensate. The reason is there is a maximum limit per VG of;
PV's * PE's size * Max_PE

eg. 54 (PV's) * 4 (default PE Size) * 2048 (Max PE) is too large. You cant or dont want to adjust PV or Max PE so adjust the PE size up (from 4 MB) this will result in this total being lower and the VG should create. Becuase its such a large VG you may need to bump up PE Size well beyond 8 (16 or 32Mb) but this will degrade performance so you should consider breaking your VG into 2 or more.

Ive been trying to find what the max limit of PVs * PE * Max_PE is for a VG but so far im unable to do so. Does anyone else know what it is ? if so you can do a simple calculation before you create your VG to see what the smallest PE size can be, then decide if its worth it.

[Patrick Wallek]

Here is the text from document KBRC00000716 in the TKB.

***************************
vgcreate error: file too large
DocId: KBRC00000716

Updated: 3/23/01 7:43:00 AM

PROBLEM

When attempting to create a new volume group with vgcreate,
an error occurs: file too large

CONFIGURATION

HP-UX 10.X, 11.X

RESOLUTION

Since the LVM data structures must fit into a single extent on
the disk, the "file too large" error occurs when the extent size is
smaller than the LVM data structures.

As disks continue to increase in size, there is not enough room
in the header files to create a table large enough to track all
the physical extents.

On the one hand, you can reduce the size of the LVM data
structure by reducing the maximum number of logical volumes
the volume group can contain (max_lv), or, the maximum
number of physical volumes the volume group can contain (max_pv).

On the other hand, you can increase the size of the physical
extents (pe_size) so that the LVM data structure will fit into a
single extent.

# vgcreate -l (number of max logical volumes) -p (number of max physical volumes) -s (size in megabytes of physical extent) /dev/vg## /dev/dsk/c#t#d#

By default, these parameters are set to:

max_lv 255
max_pv 16
pe_size 4MB