what use is virtualsize -- or how is it to be used?
I just saw it in the man page, and first thing I tried was creating a logical volume by just giving a --virtualsize, arg -- thinking it would 'auto-extend it' as needed.
Nep.
Next was looking on the net and seeing an example that gave it some small size (-L 1G),
with a virtual size of 2G. So what is that supposed to do?
I just now thought to copy a bunch of files ( that differed from yesterday to today) to a tmp partition) but had it fail miserably when it REALLY failed upon reaching the physical limit -- not the virtual limit!)....
I was trying to use rsync to copy from a snap from yesturday of /home that was mounted on /ohome to 'home.diff' (the partition that I used 'virtual size' with, ... I gave it a real size of 1G, and a virtual size of 1T.
Using rsync, I had --compare-dest=/ohome (where I mount yesturday's snap) and copied
from /home to /home.diff (the virtual partition).... Well the diffs were > 1G, so had
hoped /home.diff would expand to it's virtual size... Anyway, got I/O errors, after I ran out of space. Ok, so *that*'s not what virtual size is for...either!
Anyway, I unmounted the now 'corrupt' /home.diff, and tried to remove it... Got all sorts of i/o errors using lvremove Home.diff. (-f didn't work either).
Got it to remove with lvremove -f /dev/PV/Home.diff That gave I/O errors too, but successfully completed...
So what's virtual size good for, anyway?
Virtual size lets you create a 200G file system om a 20G LV and then lvextend as needed, without the need to resize the filesystem. Read about sparse files for ideas of other uses.
It'd like a sparse device in that blocks need not actually exist until they are written to.
It currently has a performance and flexibility impact that prevents us from using it, though we would like to.
Quoted 51 lines · Linda A. Walsh
I just saw it in the man page, and first thing I tried was creating a logical volume
by just giving a --virtualsize, arg -- thinking it would 'auto-extend it' as needed.Nep.
Next was looking on the net and seeing an example that gave it some small size (-L 1G),
with a virtual size of 2G. So what is that supposed to do?I just now thought to copy a bunch of files ( that differed from yesterday to today) to a tmp
partition) but had it fail miserably when it REALLY failed upon reaching
the physical
limit -- not the virtual limit!)....I was trying to use rsync to copy from a snap from yesturday of /home that was mounted on
/ohome to 'home.diff' (the partition that I used 'virtual size' with, ... I gave it a real
size of 1G, and a virtual size of 1T.Using rsync, I had --compare-dest=/ohome (where I mount yesturday's snap) and copied
from /home to /home.diff (the virtual partition).... Well the diffs
were > 1G, so had
hoped /home.diff would expand to it's virtual size... Anyway, got I/O errors, after I
ran out of space. Ok, so *that*'s not what virtual size is for...either!Anyway, I unmounted the now 'corrupt' /home.diff, and tried to remove it...
Got all sorts of i/o errors using lvremove Home.diff. (-f didn't work either).Got it to remove with lvremove -f
/dev/PV/Home.diffThat gave I/O errors too, but successfully completed...So what's virtual size good for, anyway?
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Quoted 5 lines · On Fri, Jul 08 2011 at 7:17pm -0400, [email protected]…
Virtual size lets you create a 200G file system om a 20G LV and then lvextend as needed, without the need to resize the filesystem. Read about sparse files for ideas of other uses.
It'd like a sparse device in that blocks need not actually exist until they are written to.
It currently has a performance and flexibility impact that prevents us from using it, though we would like to.
Please have a look at the DM thinp target that was just posted to dm-devel.
We don't have lvm2 support for this thinp target yet, we are working on it, but thinp is a much richer solution that should address your needs.
Mike
Ah...of course...
When I create the FS, it will create it the size of the existing FS, which is less efficient that calling "<fs>_extend" after each lv_extend...(presuming one is using a fs with that ability)....(do most these days? I usually just use xfs which does)...