[dm-devel] Dmsetup snapshot create/remove procedure and latest status with 2.6.x kernel series

[Hubert]

Hello,

I noticed that lvm2 create/remove snapshot of logical volume feature 
with 2.6.x kernel series is still very bad and at last randomly causes 
that any access (read/write) to that lv is impossible or even ocures 
system hung up.

In detail especially create/remove many snapshots of XFS logical volume 
is big problem and causes randomly hung up xfs_io or dmsetup 
suspend/resume calls in memory.

Please if somebody could help and give me some exemple(s) of proper use 
dmsetup tool (suspend/resume) or maybe xfs_freeze -f/u command under 
creating/removing snapshot and copying data at the same time ?

Should i use any of above dmsetup or xfs_freeze commands ?

My configuration :
- Debian GNU/Linux 3.0 stable
- tested kernels: 2.6.12.3, 2.6.13.2, 2.6.14rc1, 2.6.14rc2
- libdevmapper and lvm2 1.05 - both from cvs
- 512MB DDR RAM
- 3ware 3xxx SATA Raid controller
- 8x 250GB SATA HDD (Raid0 sda = 1.36T)
- 1x vg, 1x xfs lv = 698GB, 2x snapshot = 349GB each

I randomly creating / removing snashots under copying data from remote
host to smb share or to iSCSI target on my server.

I noticed that best results give me xfs_freeze -f/u usage but it 
sometimes couses that xfs_io hung up and then any i/o calls to XFS 
logical volume are inpossible.

Even if i add more RAM (1/2GB) it not help.

What dm-devel patches should be applied (patches 8 and 9 for snapshots 
don't make any diffrence) ?


Thanks for any help.
Best regards

Hubert


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