[linux-lvm] LVM Problems :)

Ken Fuchs kfuchs at winternet.com
Mon Feb 16 18:10:04 UTC 2004 

>> Heinz Mauelshagen wrote:

>> >the missing task was to shrink the LV.

>On Sun, Feb 15, 2004 at 12:09:46PM -0600, Ken Fuchs wrote:

>> Yes, I know.  The following does that (indirectly):
>> 
>> # resize_ext2 /<LV path>

Sorry, I didn't make it clear that the above command is only the first
of a two command sequence.  The second command of the sequence as
posted earlier and quoted further down in this message was:

# e2fsadm --extents <desired size in extents> /<LV path>

Heinz Mauelshagen wrote:

>That would grow the FS back to the LV size, not shrink it down to the FS size
>which is the intention in this particular case.

Actually, as I recall (also implied by quoted text at the end of this
message), the person who started this thread wanted to use e2fsadm(8) to
resize a ext2/ext3 filesystem/logical volume, but e2fsadm failed
complaining that the filesystem was smaller than the logical volume.
There are at least three potential solutions to this problem:

1) Grow the ext2/ext3 filesystem to fit the logical volume using
   resize_ext2(8).  The default FS size for resize_ext2 is the
   containing block device size, making this a safe and easy solution.

   # resize_ext2 /<LV path>

2) Shrink the LV to fit the current ext2/ext3 filesystem size, but
   lvreduce(8) has no awareness of the containing filesystem (if any)
   and thus can't have an option to reduce the logical volume to the fit
   the containing filesystem.

   # lvreduce --extents `<command that computes size in extents>` /<LV path>

3) Modify e2fsadm(8), so rather than failing when the ext2/ext3
   filesystem is initially smaller than the containing LV, it issues a
   warning and optionally asks whether or not to proceed.  This or a
   similar solution is probably the best.

Shrinking the LV size down to the _exact_ size of the FS may not even be
possible if the filesystem size is not an even multiple of the extent
size of the containing VG.  Thus, growing the (ext2 or ext3) filesystem
to fit the current LV size using resize_ext2(8) may be a better
preliminary step to using e2fsadm(8), since an ext2/ext3 filesystem has
a finer granularity than LVM.

The entire previous message is quoted below.

Sincerely,

Ken Fuchs <kfuchs at winternet.com>

------------------------------------------------------------------------

>On Sun, Feb 15, 2004 at 12:09:46PM -0600, Ken Fuchs wrote:
>> Heinz Mauelshagen wrote:
>> 
>> >the missing task was to shrink the LV.
>> 
>> Yes, I know.  The following does that (indirectly):
>> 
>> # resize_ext2 /<LV path>
>
>That would grow the FS back to the LV size, not shrink it down to the FS size
>which is the intention in this particular case.
>
>> 
>> Without the size argument this command resizes the ext2 or ext3
>> filesystem to fit the LV (obviating the need to calculate a new size of
>> the LV that fits the filesystem size which may not even be optimal if
>> the filesystem size is not a multiple of the extent size).
>> 
>> # e2fsadm --size <desired size> /<LV path>
>> 
>> or 
>> 
>> # e2fsadm --extents <desired size in extents> /<LV path>
>> 
>> Used to resize the LV and ext2 or ext3 filesystem in a single step.
>> 
>> The whole point of the above two step sequence is to avoid the
>> possibility of miscalculating the new size of the LV when using
>> lvreduce(8).  It is a safer, though longer way to effectively do a
>> lvreduce(8) or lvextent(8) when the contained filesystem is ext2 or
>> ext3.
>
>I know. I wrote it ;)
>
>The FS was smaller than the LV already due to some unknown problem.
>
>> 
>> In my opinion, this is a better solution when one is uncertain about the
>> correct size to use with lvreduce(8) to shrink the LV to fit either an
>> ext2 or ext3 filesystem.
>
>Absolutely users should prefer using e2fsadm doing LV + ext2/ext3 resizing
>(presumably they can, because the FS and LV have the same size).
>
>Regards,
>Heinz    -- The LVM Guy --
>
>
>> 
>> The previous message is quoted below.
>> 
>> Sincerely,
>> 
>> Ken Fuchs <kfuchs at winternet.com>
>> 
>> 
>> >On Fri, Feb 13, 2004 at 03:23:41PM -0600, Ken Fuchs wrote:
>> >> Heinz Mauelshagen wrote:
>> >> 
>> >> >the size of your filesystem and logical volume differs already.
>> >> >That's why e2fsadm fails.
>> >> >Did you eventually run resize2fs in order to shrink the filesystem ?
>> >> 
>> >> >Your logical volume size is 1091456MB (32MB/PE * 34108 PE) but your
>> >> >filesystem size is 963584GB (941GB * 1024MB/GB; check with
>> >> >"tune2fs -l" and look for the block count and block size to calculate
>> >> >this correctly).
>> >> 
>> >> >In case the result shows, that your filesystem is already smaller than the LV,
>> >> >lvreduce the logical volume appropriately.
>> >> 
>> >> >Use the block count * block size result and round it up to the next PE!
>> >> 
>> >> To avoid an error in calculating the correct number of logical extents,
>> >> and possibly doing an lvreduce(8) to a size smaller than the filesystem:
>> >> 
>> >> Use resize_ext2(8) without a size argument.  This will resize the ext2
>> >> or ext3 filesystem to be the same size as the logical volume containing
>> >> it.  After doing this, e2fsadm(8) can be used to resize the filesystem
>> >> and logical volume "simultaneously" to any desired size (that can
>> >> contain the filesystem's data).
>> >> 
>> >> Sincerely,
>> >> 
>> >> Ken Fuchs <kfuchs at winternet.com>
>> >> 
>> >> _______________________________________________
>> >> linux-lvm mailing list
>> >> linux-lvm at redhat.com
>> >> https://www.redhat.com/mailman/listinfo/linux-lvm
>> >> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>> >
>> >-- 
>> >
>> >Regards,
>> >Heinz    -- The LVM Guy --
>> >
>> >*** Software bugs are stupid.
>> >    Nevertheless it needs not so stupid people to solve them ***
>> >
>> >=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
>> >
>> >Heinz Mauelshagen                                 Red Hat, Inc.
>> >Consulting Development Engineer                   Am Sonnenhang 11
>> >                                                  56242 Marienrachdorf
>> >                                                  Germany
>> >Mauelshagen at RedHat.com                            +49 2626 141200
>> >                                                       FAX 924446
>> >=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
>> >
>> >_______________________________________________
>> >linux-lvm mailing list
>> >linux-lvm at redhat.com
>> >https://www.redhat.com/mailman/listinfo/linux-lvm
>> >read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>> >
>> 
>> _______________________________________________
>> linux-lvm mailing list
>> linux-lvm at redhat.com
>> https://www.redhat.com/mailman/listinfo/linux-lvm
>> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>
>*** Software bugs are stupid.
>    Nevertheless it needs not so stupid people to solve them ***
>
>=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
>
>Heinz Mauelshagen                                 Red Hat, Inc.
>Consulting Development Engineer                   Am Sonnenhang 11
>                                                  56242 Marienrachdorf
>                                                  Germany
>Mauelshagen at RedHat.com                            +49 2626 141200
>                                                       FAX 924446
>=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
>
>_______________________________________________
>linux-lvm mailing list
>linux-lvm at redhat.com
>https://www.redhat.com/mailman/listinfo/linux-lvm
>read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

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