[linux-lvm] Contiguous policy causes lvextend problems

[David Greaves <david@dgreaves.com>]

Hi

Summary:
I had a problem trying to extend an lv. It turns out that it was due to 
having a contiguous allocation policy.
The error report wasn't helpful :)
Maybe this will help others searching the archive (I couldn't find 
anything useful)
Maybe someone could point me at what contiguous does?


so, I recently had a problem trying to lvextend an lv:

root@bao:~ # lvextend -l +2086 /dev/vg1/Myth
  Extending logical volume Myth to 401.69 GB
  Insufficient allocatable extents (4341) for logical volume Myth: 6427 
required

Everything was setup correctly:
root@bao:~ # vgdisplay
  --- Volume group ---
  VG Name               vg1
  System ID            
  Format                lvm2
  Metadata Areas        2
  Metadata Sequence No  3
  VG Access             read/write
  VG Status             resizable
  MAX LV                255
  Cur LV                1
  Open LV               1
  Max PV                255
  Cur PV                2
  Act PV                2
  VG Size               401.69 GB
  PE Size               64.00 MB
  Total PE              6427
  Alloc PE / Size       4341 / 271.31 GB
  Free  PE / Size       2086 / 130.38 GB
  VG UUID               T1gURQ-6CZM-axdh-UAHa-E1nd-fxEC-cwDLdq
  
root@bao:~ # pvdisplay
  --- Physical volume ---
  PV Name               /dev/hdc3
  VG Name               vg1
  PV Size               271.31 GB / not usable 0  
  Allocatable           yes (but full)
  PE Size (KByte)       65536
  Total PE              4341
  Free PE               0
  Allocated PE          4341
  PV UUID               25Ngo9-LGNo-0Nsp-R826-C1Lc-5pD7-xh3GOX
  
  --- Physical volume ---
  PV Name               /dev/hde2
  VG Name               vg1
  PV Size               130.38 GB / not usable 0  
  Allocatable           yes
  PE Size (KByte)       65536
  Total PE              2086
  Free PE               2086
  Allocated PE          0
  PV UUID               22hSvz-eARY-1AAq-5kko-whHH-QJRl-s94us5
  
  --- NEW Physical volume ---
  PV Name               /dev/hdc
  VG Name              
  PV Size               279.40 GB
  Allocatable           NO
  PE Size (KByte)       0
  Total PE              0
  Free PE               0
  Allocated PE          0
  PV UUID               PWxvHH-uary-DgTx-Mk9K-UfoM-4gCs-fR1vzo
  
root@bao:~ # lvdisplay
  --- Logical volume ---
  LV Name                /dev/vg1/Myth
  VG Name                vg1
  LV UUID                4hzmiM-9uSn-67Lm-ZWzS-YS2Q-gVtm-8HbTWW
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                271.31 GB
  Current LE             4341
  Segments               1
  Allocation             contiguous
  Read ahead sectors     0
  Block device           254:0

but the allocation policy was 'contiguous'.
This isn't documented (that I could find) in the man pages - I am 
creating large (3-4Gb) files from a PVR and thought I'd try contiguous 
(in a kind of "what the heck, sounds about right" kinda way)
It turns out that I needed to:
root@bao:~ # lvchange -C n /dev/vg1/Myth
  Logical volume "Myth" changed
root@bao:~ # lvextend -l +2086 /dev/vg1/Myth
  Extending logical volume Myth to 401.69 GB
  Logical volume Myth successfully resized

Maybe a better error (or documentation of -C) is needed?

David