[linux-lvm] understanding large LVM volumes
Randall A. Jones
rajones at svs.gsfc.nasa.gov
Sat Jan 15 17:25:38 UTC 2005
>>>How does the Physical Extent size affect the maximum VG size?
>>>How does one go about chosing a PE size for a VG?
>Those limits (65536 LE per LV) does not apply to LVM 2 and 2.6 kernel.
>Your LV can have MUCH more LE (I dont know if there is even reachable
>limit for this). One and only feedback (if you can notice this) is
>that userspace programs for managing LVM works _little_ slower, when
>there is enormous number od LE to administrate.
>I tested it with 4GB LV on 16MB LE (but I didnt see difference)
I figured that this limitation was gone in LVM 2, but I have not read
And, as Stephane pointed out, the man page for vgcreate states the
limits which created more confusion for me.
I was able to create a single LV from my 4.3TB VG. There are 1134586 PE
in this one LV.
Now I understand why this is possible in LVM 2.
What I am still not sure about is how to choose a PE size for this large VG.
What are the benefits of a small PE size compared to a large PE size?
As mentioned, it does seem like a larger PE might be more efficient
since there are fewer LEs per LV to manage.
Are there any other benefits?
>>But think hard about it....
>>Are you sure you can't "logicaly" split it ? and that the 10 TB of
>>data will concern the same software or pool of user and so on ?
>>Are you sure you will not have to move only a part of the data one day ?
>>(add a new server and need to export some of the data to import it
>>to the new server ?)
>>Also think about how you will (if you need) backup the whole thing...
>When I create logical structure of my LVM diskspace, I always think
>about those things:
>1) Never assign ALL your disks at once between VGs.
>You can ALWAYS add disk later to vg, according to your needs. Removing
>involves pvmove, whitch is more stressing then vgextend. (of course,
>if U have more, then 5-6 disks). And almost all filesystems support
>extending of FS, but not all like shrinking.
>2) Never create BIG vg, unless they are base on raid disks.
>Damage of one disk whitch is not in RAID, damages VG (of course, U
>can recreate structure of vg by clonig PV ID, but filesystems will be
>damaged - mabye in more then one LV.)
There is a lot of redundancy built into our data archives; RAID-5, hot
spare drives, cold spare drives, huge tape backup, off site tape
backup. This is the first time an archive will grow over the 32 bit,
pre LBD, 2TB limit.
I just want to make sure I get the setup correct and that I understand
all the possibilities before we commit to a configuration. Recreating a
10TB data store after the data is present takes a *long* time.
Thank you for all the info and discussion.
Randall Jones GST NASA Goddard Space Flight Center
HPC Visualization Support http://hpcvis.gsfc.nasa.gov
Scientific Visualization Studio http://svs.gsfc.nasa.gov
rajones at svs.gsfc.nasa.gov Code 610.3 301-286-2239
More information about the linux-lvm