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VVR enables you to verify that the data on the Secondary is identical to the data on the Primary data volumes, either when the application is active or inactive. VVR provides the following methods to verify the data at the Secondary site: online data verification and offline data verification.
Online data verification allows you to validate the data even when replication is in progress. In this method instead of the actual volumes, the point-in-time snapshots are compared. This method is referred to as online data verification.
Offline data verification can be performed only when replication is not active. If you have already created the Primary and Secondary volumes and replication is in progress, you need to pause replication and then perform data validation between the corresponding Primary and Secondary volumes to make sure that the data volumes on the Primary and Secondary are the same. To do this, use the vradmin syncrvg command with the -verify option. To use this command for verifying the data, the Secondary must be up-to-date. This command performs a comparison of the checksums on the corresponding Primary and Secondary volumes.
You can also validate the data on new data volumes before adding them to an RDS. For information, refer to Verifying the data on the Primary and Secondary volumes.
The space-optimized snapshots that are created using the vxrvg snapshot command can be used to verify whether the data on the Primary and Secondary RVG volumes is the same.
The major advantage of this feature over the vradmin -verify syncrvg command is that you do not need to stop the replication. The verification can be done even while the replication is in progress because the point-in-time snapshots, and not the volumes, are compared. This feature is very useful if you want to check the integrity of the data volumes on the Secondary when replication is in progress.
The vradmin verifydata command creates the space-optimized snapshots on the Primary and the Secondary before it proceeds with performing online data verification. The vradmin verifydata command also ensures that the snapshots are taken only after the replication has been paused using the vxibc freeze command. As a result there may be a momentary pause in the replication. It is necessary to freeze the writes so that the snapshots can be taken at an identical point in replication time, on each of the required hosts.
The vradmin verifydata then verifies the data between the remote and local hosts by comparing the space-optimized snapshots.
To perform online data verification, use the command:
vradmin [-g diskgroup] [-k {cache|snap}] verifydata rvg_name \
sechost {cache=cacheobj | cachesize=size}
The attribute sechost specifies the name of the Secondary host.
The cache attribute specifies a name for the precreated cache object, on which the snapshots for the volumes in the specified RVG will be created. The cachesize attribute specifies a default size for the cache object with respect to the source volume. If the RVG on either the Primary or the Secondary has VxVM ISP volumes, then you cannot use the cachesize attribute.
You must specify only one of these attributes at one time for the command to create a cache object for each snapshot.
This command performs the following tasks:
By default, the vradmin verifydata command destroys the snapshot volume and the cache object after the data verification has proceeded successfully. However, if you want to preserve the snapshot volumes then you must use the vradmin verifydata command with the -k snap option. If you want to preserve the cache object then use the vradmin verifydata command with the -k cache option. The same cache object can then be reused when creating future snapshots. You cannot use the -k option if you have used the cachesize option, as it is an invalid combination and the command fails with an error message. Note that when specifying the -k option you must specify either the cache or the snap argument with it.
Note
When the -k snap option is specified the cache object is also preserved along with the snapshot since the snapshot cannot exist without the cache object.
VVR also provides you with sample scripts that can be used to freeze the replication and then take instant space-optimized snapshots. For details, refer to Sample scripts.
rvg_name sechost {cache=cacheobj | cachesize=size}
VVR enables you to verify whether the data on the Secondary is identical to the data on the Primary data volumes when the application is inactive. The vradmin syncrvg command with the -verify option verifies and reports any differences between the data volumes associated with the Secondary RVG and the corresponding Primary RVG. If a volume set is associated to the RDS, the vradmin -verify syncrvg command verifies only the component volumes that are associated to the RVG. The vradmin -verify syncrvg command only reports whether the Primary and Secondary volumes are identical or not. It does not make them identical. As the command runs, it reports the progress every 10 seconds. An MD5 checksum is used to calculate the difference between the Primary and the Secondary data volumes. Refer to Using difference-based synchronization.
Prerequisitefor using the vradmin -verify syncrvg command
All applications using the Primary data volumes must be stopped before running the vradmin -verify syncrvg command.
To verify the differences between the Primary and Secondary data volumes
# vradmin -g diskgroup -verify syncrvg local_rvgname \
When this command is invoked, you are prompted to confirm that the Primary data volumes are not in use. You can use the -s option to skip this confirmation step.
The argument local_rvgname is the name of the RVG on the local host and represents the RDS.
The argument sec_hostname is a space-separated list of the names of the Secondary hosts as displayed in the output of the vradmin printrvg command.
This command checks the status of the Primary RLINK to each of the Secondary RVGs being verified. If any of the RLINKs are not up-to-date, the vradmin -verify syncrvg command returns with a message to indicate that the RLINKs are not up-to-date. In this scenario, verification is not be performed. Use the vxrlink status command to determine the extent to which the Secondary is behind.
To verify the data differences between the Primary RVG hr_rvg on seattle and the Secondary RVG on host london, issue the following command from any host in the RDS:
# vradmin -g hrdg -verify syncrvg hr_rvg london
The output resembles the following if the Primary and Secondary data volumes
are identical:
VxVM VVR vxrsync INFO V-5-52-2210 Starting volume verification to remote
VxVM VVR vxrsync INFO V-5-52-2211 Source host: 10.182.136.192
VxVM VVR vxrsync INFO V-5-52-2212 Destination host(s): 10.182.136.193
VxVM VVR vxrsync INFO V-5-52-2213 Total volumes: 1
VxVM VVR vxrsync INFO V-5-52-2214 Total size: 4.000 G
Eps_time Dest_host Src_vol Dest_vol F'shed/Tot_sz Diff Done
00:00:00 10.182.136.193 hr_dv hr_dv 0M/4096M 0% 0%
00:00:10 10.182.136.193 hr_dv hr_dv 221M/4096M 0% 5%
00:00:20 10.182.136.193 hr_dv hr_dv 468M/4096M 0% 11%
00:00:30 10.182.136.193 hr_dv hr_dv 705M/4096M 0% 17%
00:00:40 10.182.136.193 hr_dv hr_dv 945M/4096M 0% 23%
00:00:50 10.182.136.193 hr_dv hr_dv 1184M/4096M 0% 29%
00:01:00 10.182.136.193 hr_dv hr_dv 1419M/4096M 0% 35%
00:01:10 10.182.136.193 hr_dv hr_dv 1655M/4096M 0% 40%
00:01:20 10.182.136.193 hr_dv hr_dv 1886M/4096M 0% 46%
00:01:30 10.182.136.193 hr_dv hr_dv 2124M/4096M 0% 52%
00:01:40 10.182.136.193 hr_dv hr_dv 2356M/4096M 0% 58%
00:01:50 10.182.136.193 hr_dv hr_dv 2590M/4096M 0% 63%
00:02:00 10.182.136.193 hr_dv hr_dv 2838M/4096M 0% 69%
00:02:10 10.182.136.193 hr_dv hr_dv 3091M/4096M 0% 75%
00:02:20 10.182.136.193 hr_dv hr_dv 3324M/4096M 0% 81%
00:02:30 10.182.136.193 hr_dv hr_dv 3564M/4096M 0% 87%
00:02:40 10.182.136.193 hr_dv hr_dv 3809M/4096M 0% 93%
00:02:50 10.182.136.193 hr_dv hr_dv 4070M/4096M 0% 99%
00:02:51 10.182.136.193 hr_dv hr_dv 4096M/4096M 0% 100%
VxVM VVR vxrsync INFO V-5-52-2217 The volumes are verified as identical.
VxVM VVR vxrsync INFO V-5-52-2219 VxRSync operation completed.
VxVM VVR vxrsync INFO V-5-52-2220 Total elapsed time: 0:02:51
If there are differences in the data volumes, the output looks similar to the one shown below:
VxVM VVR vxrsync INFO V-5-52-2210 Starting volume verification to remote
VxVM VVR vxrsync INFO V-5-52-2211 Source host: 10.182.136.192
VxVM VVR vxrsync INFO V-5-52-2212 Destination host(s): 10.182.136.193
VxVM VVR vxrsync INFO V-5-52-2213 Total volumes: 1
VxVM VVR vxrsync INFO V-5-52-2214 Total size: 4.000 G
Eps_time Dest_host Src_vol Dest_vol F'shed/Tot_sz Diff Done
00:00:01 10.182.136.193 hr_dv hr_dv 0M/4096M 0% 0%
00:00:11 10.182.136.193 hr_dv hr_dv 231M/4096M 48% 6%
00:00:21 10.182.136.193 hr_dv hr_dv 476M/4096M 23% 12%
00:00:31 10.182.136.193 hr_dv hr_dv 719M/4096M 15% 18%
00:00:41 10.182.136.193 hr_dv hr_dv 954M/4096M 12% 23%
00:00:51 10.182.136.193 hr_dv hr_dv 1202M/4096M 9% 29%
00:01:01 10.182.136.193 hr_dv hr_dv 1438M/4096M 8% 35%
00:01:11 10.182.136.193 hr_dv hr_dv 1680M/4096M 7% 41%
00:01:21 10.182.136.193 hr_dv hr_dv 1924M/4096M 6% 47%
00:01:31 10.182.136.193 hr_dv hr_dv 2165M/4096M 5% 53%
00:01:41 10.182.136.193 hr_dv hr_dv 2418M/4096M 5% 59%
00:01:51 10.182.136.193 hr_dv hr_dv 2668M/4096M 4% 65%
00:02:01 10.182.136.193 hr_dv hr_dv 2906M/4096M 4% 71%
00:02:11 10.182.136.193 hr_dv hr_dv 3140M/4096M 4% 77%
00:02:21 10.182.136.193 hr_dv hr_dv 3386M/4096M 3% 83%
00:02:31 10.182.136.193 hr_dv hr_dv 3630M/4096M 3% 89%
00:02:41 10.182.136.193 hr_dv hr_dv 3881M/4096M 3% 95%
00:02:49 10.182.136.193 hr_dv hr_dv 4096M/4096M 3% 100%
VxVM VVR vxrsync INFO V-5-52-2218 Verification of the remote volumes found
VxVM VVR vxrsync INFO V-5-52-2219 VxRSync operation completed.
VxVM VVR vxrsync INFO V-5-52-2220 Total elapsed time: 0:02:50