EVMS 2.5.4 snapshot on Linux 2.6.20

Hi all,

We are  using EVMS 2.5.4 version on Linux kernel version 2.6.16 along.
It was working fine. For some of the other performance reasons, we had
to move to Linux 2.6.20 version - specifically we are currently on
2.6.20-rc6 version.

We are observing that the snapshots are not getting created
successfully in this kernel version. Have anyone successfully created
a snapshot in this kernel version yet? We also tried to backtrack the
kernel version to 2.6.19.1 but in vain - snapshots are not getting
created but the rest of the EVMS is working fine. Are there any
EVMS/Kernel/DM patches required on this specific kernel version?

When we create the snapshots, we observe that the snapshot object is
getting successfully created (when we do a query:output) but the
corresponding node is not getting created in (/dev/evms/.nodes) that
we want to mount for accessing the snapshot contents.

We tried to do the following couple of items after going through
*somewhat related issues* reported in the EVMS mail archives but we
did not observe any change in the behavior:

a) Going by ( http://marc.theaimsgroup.com/?l=evms-devel&m=112699668724855&w=2)
as suggested by Kevin, we modified the drivers in the kernel source
tree drivers/dm/dm-snap.c and changed the value of SNAPSHOT_PAGES to
be that of 64 instead of the currently 256.
b) Going by (http://marc.theaimsgroup.com/?l=evms-devel&m=114536935000036&w=2
), we removed the O_DIRECT flag in plugins/disk/localdskmgr.c while
opening the node.

Both these changes in the 2.5.4 code base refused to make any changes
in the observed behavior. This is what we attempted to do for creating
the snapshots. We have also attached a detailed ('debug' log) for the
EVMS commands that we used.

We would really appreciate if someone can give us a few thoughts on
what we are missing to do as we have been raking our brains on this
for quite some time now....

Sequence of commands that we had given on the EVMS command line:

echo "Create:Region,LVM2={name=Reg__SNAPtestsnapregion,size=1.00GB},
lvm2/raid1/Freespace" | evms -s -d debug

echo "Create:object,Snapshot=
{original=/dev/evms/siva,snapshot=SNAP__testsnap,Writeable=true},lvm2/raid1/Reg__SNAPtestsnapregion"|
evms -s -d debug

After running the above two commands, the following is the output of
query objects EVMS command (This output is showing the snapshot object
created above):

-bash-3.00# echo q:o | evms

EVMS Command Line Interpreter Version 2.5.4

EVMS:
Logical Disk Name: sda
Major: 8
Minor: 0
Active: TRUE
Logical Disk Size:
465.76 GB
Logical Disk Geometry: 60801 Cylinders, 255 Heads, 63 Sectors per Track,
512 Bytes per Sector
LBA of the 1024 Cylinder Limit: 16434495

Logical Disk Name: sdb
Major: 8
Minor: 16
Active: TRUE

Logical Disk Size: 465.76 GB
Logical Disk Geometry: 60801 Cylinders, 255 Heads, 63 Sectors per Track,
512 Bytes per Sector
LBA of the 1024 Cylinder Limit: 16434495

Logical Disk Name: sdc
Major: 8

Minor: 32
Active: TRUE
Logical Disk Size: 496.00 MB
Logical Disk Geometry: 63 Cylinders, 16 Heads, 62 Sectors per Track, 512
Bytes per Sector
LBA of the 1024 Cylinder Limit: 1015808

Segment Name: sda_mbr

Major: 0
Minor: 0
Active: FALSE
Segment Size: 31.50 KB
Starting LBA: 0
Segment Type: Metadata

Segment Name: sda1
Major: 253
Minor: 1
Active: TRUE
Segment Size: 465.76 GB
Starting LBA: 63

Segment Type: Data

Segment Name: sda_freespace1
Major: 0
Minor: 0
Active: FALSE
Segment Size: 2.49 MB
Starting LBA: 976768065
Segment Type: Freespace

Segment Name: sdb_mbr
Major: 0

Minor: 0
Active: FALSE
Segment Size: 31.50 KB
Starting LBA: 0
Segment Type: Metadata

Segment Name: sdb1
Major: 253
Minor: 0
Active: TRUE
Segment Size: 465.76 GB
Starting LBA: 63
Segment Type: Data


Segment Name: sdb_freespace1
Major: 0
Minor: 0
Active: FALSE
Segment Size: 2.49 MB
Starting LBA: 976768065
Segment Type: Freespace

Segment Name: sdc_mbr
Major: 0
Minor: 0
Active: FALSE

Segment Size: 31.00 KB
Starting LBA: 0
Segment Type: Metadata

Segment Name: sdc1
Major: 0
Minor: 0
Active: FALSE
Segment Size: 495.97 MB
Starting LBA: 62
Segment Type: Data

Region Name: lvm2/raid1/Reg__SNAPtestsnapregion

Major: 253
Minor: 8
Active: TRUE
Region Size: 1.00 GB
Region Type: Data

Region Name: lvm2/raid1/Regshare1
Major: 253
Minor: 2
Active: TRUE
Region Size: 20.00 GB
Region Type: Data

Region Name: lvm2/raid1/Regshare2
Major: 253
Minor: 4
Active: TRUE
Region Size:
20.00 GB
Region Type: Data

Region Name: lvm2/raid1/Regsiva
Major: 253
Minor: 9
Active: TRUE
Region Size: 1.00 GB
Region Type: Data

Region Name: lvm2/raid1/Freespace
Major: 0
Minor: 0

Active: FALSE
Region Size: 423.75 GB
Region Type: Freespace

Region Name: md/md0
Major: 9
Minor: 0
Active: TRUE
Region Size: 465.76 GB
Region Type: Data

Object Name: SNAP__testsnap
Major: 0

Minor: 0
Active: FALSE
Object Size: 1024.00 MB

Object Name: lvm2/raid1/Regsiva#origin#
Major: 253
Minor: 6
Active: TRUE
Object Size: 1.00 GB

After analyzing the above log file, we saw that the activate snap was
returning with an error message but not sure of whether the failure is
because of this error message and if so, what should we do to correct
this? The below is the referred extract from this log file that we are
referring:

/********************** POSSIBLE ERROR MESSAGE ***************************/
Feb 06 18:54:25 sanat _7_ Snapshot: activate_snapshot: Exit.  Return value
= 22
Feb 06 18:54:25 sanat _7_ Snapshot: snap_activate: Exit.  Return value = 22

Feb 06 18:54:25 sanat _8_ Engine: activate_object:
activate(SNAP__testsnap) returned 22: Invalid argument
Feb 06 18:54:25 sanat _7_ Engine: activate_object: Exit.  Return value is 22.
Feb 06 18:54:25 sanat _3_ Engine: activate: Error code 22 activating

object SNAP__testsnap: Invalid argument
/***********************POSSIBLE ERROR MESSGAE***************************/


Please help.

Thanks,

Srini

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