Booting - Enterprise Volume Management System

[Toby Kelsey]

Alexander Skwar wrote:

> Toby Kelsey <toby_kelsey at ntlworld.com>:


>>Interesting.  Looking at the HOWTO, it seems that LVM combines the main 
>>disadvantage of separate partitions - having to manually unmount and resize when 
>>you run out of space
> 
> 
> unmount? Have you actually read the howto?

Perhaps you should try reading it.

"  ext2/ext3

Unless you have patched your kernel with the ext2online patch it is necessary to 
unmount the file system before resizing it."

Reiserfs, xfs and jfs can be grown mounted, but reiserfs is slower and allegedly 
buggier than other filesystems, and xfs and jfs are unsuitable for LVM as I have 
mentioned already.

>>- with the main disadvantage of one big partition -  
>>allowing fs corruption and installers to affect user and system data together. 
> 
> 
> What are you talking about?

You don't think there are any disadvantages of one big partition?  Why even 
bother with LVM on a single disk if you can just make one big partition?

>>The main advantage appears being able to resize logical volumes and filesystems 
>>easily, but for jfs "this is extremely error prone"
> 
> 
> How so? mount -o remount,resize /your/jfs

Perhas you know better than the HOWTO:

"Known Kernel Bug

Some kernel versions have problems with this syntax (2.6.0 is known to have this 
problem). In this case you have to explicitly specify the new size of the 
filesystem in blocks. This is extremely error prone as you must know the 
blocksize of your filesystem and calculate the new size based on those units. "

Until "some kernels" are identified or fixed it is not safe.  I am not going to 
continue pasting blocks of text from the HOWTO every time you profess ignorance. 
  Please read it.

>>and even for ext2/3 "there  
>>is currently no e2fsadm equivalent for LVM 2
> 
> 
> True, but ext3 can be made larger online, AFAIK. I don't use ext3, though.

With a kernel patch which is judged "rather dangereous" as I already said.
If you only use reiserfs anyway then LVM is more useful.

>>Since you cannot shrink xfs and jfs the main functionality becomes  
>>useless for many advanced users.
> 
> 
> Wrong. Mostly, filesystems will grow. It's, in my experience, quite
> rare, that filesystems need to be made smaller.

You can grow and move partitions with parted anyway, so LVM has no advantage if 
that's what you restrict it to.  Of course you can also use LVM with multiple 
disks, and it has a genuine advantage there.  I suspect it is not as fast as 
using specific software or hardware RAID though, and the HOWTO says striping 
with LVM can actually reduce performance if you have more than one LV per disk.

>>While it may be useful for servers, with confidence-building statements like "it 
>>seems that the online resizing patch is rather dangerous" I would suggest it is 
>>not yet suitable for a home or laptop system.
> 
> 
> Wrong. On what experience do you base your conclusion? On your false reading?

Based on the HOWTO.  Please read it.

LVM has its place if you know what you are doing (and have multiple disks with 
partitions which grow and never shrink), but the "LVM is good for everybody, 
even laptop users" rhetoric I responded to was OTT.

Toby