Fixing 'segmentation fault' error while extending a striped logical volume

The purpose of this post is twofold.

First to fix 'segmentation fault' error.
Second to partially convert a striped logical volume to a linear logical volume online.

To partially convert a striped logical volume to a linear logical volume is fairly simple.
While running lvextend command specify num_stripes (i) value equal to 1.
This makes the extended size of the LV span in a linear fashion.

Yesterday I came across an issue while extending a striped logical volume strLV1.

[root@linuxserver ~]# lvs --segment vg
  LV      VG       Attr   #Str Type    SSize
  strLV0 vg -wi-ao    4 striped 205.00G
  strLV1 vg -wi-ao    4 striped 172.00G

The LV was striped across four disks. I had to extend this volume but did not have another four disks to span it on.
So I decided to do away with the stripe & span the additional space linearly.

[root@linuxserver ~]# lvextend -i1 -L +99G /dev/mapper/vg-strLV1
  Extending logical volume strLV1 to 271.00 GB
Segmentation fault

So, I got a segmentation fault error wich was a first time.

If I tried to extend the volume keeping the stiped layout in space I would've gotten the following error:

[root@linuxserver ~]# lvextend  -L +99G /dev/mapper/vg-strLV1
  Using stripesize of last segment 1.00 MB
  Extending logical volume strLV1 to 271.00 GB
  Insufficient suitable allocatable extents for logical volume strLV1: 19420 more required

After a lot of thinking I tried to apply the fundamental meaning of 'segmentation fault' to my scenario.
The system was trying to access a location that did not exist.

I then then ran lvextend command again & this time gave the disk name after the volume name to direct the expansion on the particular disk & this fixed the issue:

'df -h' before expansion:

[root@linuxserver ~]# df -h /FS
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg-strLV1
                      170G   57G  105G  35% /FS

  Logical volume strLV1 successfully resized
[root@linuxserver ~]# lvextend -i1 -L +94G /dev/mapper/vg-strLV1 /dev/mapper/mpath106
  Extending logical volume strLV1 to 272.00 GB
  Logical volume strLV1 successfully resized

[root@linuxserver ~]# resize2fs /dev/mapper/vg-strLV1
resize2fs 1.39 (29-May-2006)
Filesystem at /dev/mapper/vg-strLV1 is mounted on /FS; on-line resizing required
Performing an on-line resize of /dev/mapper/vg-strLV1 to 71303168 (4k) blocks.
The filesystem on /dev/mapper/vg-strLV1 is now 71303168 blocks long.

[root@linuxserver ~]# df -h /FS
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg-strLV1
                      268G   57G  198G  23% /FS

The LV will look something like this after the expansion:

[root@linuxserver ~]# lvs --segments vg
  LV      VG       Attr   #Str Type    SSize
  strLV0 vg -wi-ao    4 striped 205.00G
  strLV1 vg -wi-ao    4 striped 172.00G
  strLV1 vg -wi-ao    1 linear   99.00G


Note: This procedure is a fix for a bad situation. You will lose performance once the stripe goes linear. Under normal circumstances you should always try to keep the striped layout intact.