LVM extent size Post: 302477942

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Operating Systems Linux LVM extent size Post 302477942 by HansHenderson on Tuesday 7th of December 2010 04:31:06 AM

12-07-2010

Registered User

The information both of you are probably referring to is also no longer relevant for LVM2, lots of misinformation out there.

Again, sorry I can't enter URLs, but this is from IBM in 2007. Google on the literal phrase in quotes to confirm.

>With LVM2, there's no limit on the maximum numbers of extents per PV/LV.

<snip>

> there is no I/O performance penalty for smaller/bigger extent size. LVM tools usage, however, can suffer from high extent count, so using bigger extents can keep the extent count low.

---------

Note this source also gives the default as 4MB, which I believe is no longer true, as per my previous quote.

In some cases, I've seen people talk about multiple-GB-sized extents.

Personally I plan to use 1GB: 4096*256=1048576

This makes it easy to use extents directly as units in allocating space. Even 10 GB would only be 2% of the smallest drive I'm using, so wouldn't hamper flexibility, but IMO this seems a bit "out there".

==================

My main point in all this is that an "rtfm" response is inappropriate for this topic area; I have been unable to find canonical docs that directly address these issues, and there is a lot of conflicting information from what appears to be authoritative sources, even relatively recent ones.

It would be great if someone with access to some big drives would do some hands-on testing to check and post back here. Next time I have the chance I'll try to remember to do so. . .

---------- Post updated at 04:31 PM ---------- Previous update was at 07:36 AM ----------

I've posted to the linux-LVM mailing list, frequented by Neil Brown and the other LVM maintainers, in order to get more "canonical" information on these issues

Here's my attempt to bypass the URL blocking feature of this board:

http - fossplanet.com

f13/%5Blinux-lvm%5D-configuring-extent-size-83253/

If that doesn't work for you, google on

"apparently authoritative but conflicting information"

If given multiple list archive servers, I recommend fossplanet.com

The subject header is: [linux-lvm] Configuring extent size

HansHenderson

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LEARN ABOUT NETBSD

pvdisplay

PVDISPLAY(8)						      System Manager's Manual						      PVDISPLAY(8)

NAME

       pvdisplay - display attributes of a physical volume

SYNOPSIS

       pvdisplay [-c|--colon] [-d|--debug] [-h|-?|--help] [-s|--short] [-v[v]|--verbose [--verbose]] PhysicalVolumePath [PhysicalVolumePath...]

DESCRIPTION

       pvdisplay allows you to see the attributes of one or more physical volumes like size, physical extent size, space used for the volume group
       descriptor area and so on.

       pvs (8) is an alternative that provides the same information in the style of ps (1).

OPTIONS

       See lvm for common options.

       -c, --colon
	      Generate colon separated output for easier parsing in scripts or programs.  N.B. pvs (8) provides considerably more control over the
	      output.

	      The values are:

	      * physical volume device name
	      * volume group name
	      * physical volume size in kilobytes
	      * internal physical volume number (obsolete)
	      * physical volume status
	      * physical volume (not) allocatable
	      * current number of logical volumes on this physical volume
	      * physical extent size in kilobytes
	      * total number of physical extents
	      * free number of physical extents
	      * allocated number of physical extents

       -s, --short
	      Only display the size of the given physical volumes.

       -m, --maps
	      Display the mapping of physical extents to logical volumes and logical extents.

SEE ALSO

       lvm(8), pvcreate(8), lvcreate(8), vgcreate(8)

Sistina Software UK					 LVM TOOLS 2.02.44-cvs (02-17-09)					      PVDISPLAY(8)

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