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Most resizing HOWTOs for LVM don't use this command, probably because it was added in the last few years, but that may be no bad thing.
Shrinking an LVM logical volume and FS can be dangerous if you don't get the sizes exactly right, and I'm not 100% confident that the --resizefs feature is bug free. (See http://www.debuntu.org/how-to-install-ubuntu-over-lvm-fil... for a long discussion of issues, and the resizing part of http://serverfault.com/questions/279571/lvm-dangers-and-c...
Generally I have more confidence that Gparted (or parted) will not mess things up.
Fedora and LVM
Posted Nov 2, 2012 14:27 UTC (Fri) by agk (guest, #23332)
Which is why --resizefs exists: so that appropriate sizes are used and the steps are performed in the right order. The feature is fully supported.
> and I'm not 100% confident that the --resizefs feature is bug free.
"Bug free" will never be promised, of course:) The bugs you referenced look to be from before the code was included in lvm2 and were of the "feature gives an error and stops instead of resizing" variety.
Posted Nov 2, 2012 17:09 UTC (Fri) by paulj (subscriber, #341)
Posted Nov 2, 2012 17:20 UTC (Fri) by nybble41 (subscriber, #55106)
Posted Nov 5, 2012 12:08 UTC (Mon) by paulj (subscriber, #341)
That I do it that way is probably cause I pretty much never shrink fses, and the last time I had to do this was way back, when LVM was still newish and e2fsadm and/or the --resize option didn't exist, or didn't handle this.
Generally LVM lets me manage fses in such a way that I only allocate to them what is reasonable for the foreseeable future. I keep the extra space free in the VG. As/when fses need more space, I just extend them. That this is so painless to do with LVM and resize2fs - online and without interruption - makes it the best way to manage storage, I find.
So so so so much better than the olden days, when you had to rejiggle partitions, reboot several times, and potentially use your swap device as a temporary root, in order to shift space to where you needed it. That was hair-raising, and I never want to go back to that! There isn't much to LVM, it didn't take much to learn, and it's removed a lot of stress.
One lesson though: snapshots need attentive monitoring. Never let a snapshot get anywhere near full, otherwise you risk it getting full and your box will wedge! Also, the early implementations of pvmove were very risky. Apparently those problems have been ironed out and it's now a lot more reliable, but I'm conservative and tend to avoid it. Luckily, that's easy - just move PVs the old fashioned way, copy them like you had to do with FSes before LVM. ;)
Overall though, LVM is a massive win over what went before.
Posted Nov 5, 2012 12:23 UTC (Mon) by Cato (subscriber, #7643)
Re the "olden days" scenario: now that 2 to 3 TB external drives are very cheap, and USB3 or eSATA are very fast, you can simply backup all the partitions involved (a good idea anyway) to the drive, then repartition destructively and restore. (If you are using rsnapshot you only do an incremental backup since the overnight one, which will not take so long.)
This backup/restore model may be faster than doing the Gparted model of moving FSs to new location, as it uses 2 spindles not one. It also has the benefit of defragging your FSs - I know Linux FSs don't need defragging in theory, but in practice it will help somewhat particularly if FS has been in use for some years. (LVM's model will tend to increase fragmentation somewhat as you never do this sort of FS re-creation.)
I don't see why more than one reboot is needed with Gparted.
Posted Nov 5, 2012 12:32 UTC (Mon) by paulj (subscriber, #341)
That single reboot with gparted is still 1 more reboot than I need with LVM. Further, on an ongoing basis, it means you will need a lot more reboots than I will.
Posted Nov 2, 2012 18:02 UTC (Fri) by Cato (subscriber, #7643)
While you are here: I think that the LV size should be larger than the FS size by 2 x the LVM physical extent (PE) size. Is that correct?
Posted Nov 3, 2012 1:28 UTC (Sat) by agk (guest, #23332)
The LVM HOWTO at tldp hasn't been updated for several years.
> I think that the LV size should be larger than the FS size by 2 x the LVM physical extent (PE) size. Is that correct?
No. Where did that idea come from? LVM doesn't reserve any space *inside* the LVs it creates! The filesystem can use the entire LV if it wants to.
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