How to run dcscan to validate a Backup Exec Deduplication Storage Folder or a specific container within the folder.

Problem

Need to verify that the Deduplication Storage Folder is not corrupted.

If a container file (.bin) is suspected of being corrupted, or if it is necessary to find out which of two files is the best one to keep, the dcscan program can be used to check the contents of the .bin files in question.

Cause

If a container file (.bin) is suspected of being corrupted, or if it is necessary to find out which of two files is the best one to keep, the dcscan program can be used to check the contents of the .bin files in question.

Solution

The dcscan.exe program can be used to validate the contents of a Deduplication Storage Folder as a whole, or just to validate a particular container.  Please note that a rough estimate on the amount of time it takes to run dcscan is one hour per terabyte of data.  This time will also be affected by the speed of the system and the speed of the disk subsystem.  So, on a 24 terabyte deduplication folder, this could easily take 24 hours to run.

The dcscan.exe program can run while the Deduplication Storage Folder is online and being used, but it will have a performance impact.  It is also necessary to temporarily turn off compaction on the Deduplication Storage Folder to prevent false errors from being reported.  It is important to remember to turn compaction back on as described below.

When the Deduplication Storage Folder is online (Backup Exec Deduplication Manager / Engine services started)

1. Disable Lockdown settings.

To disable the Lockdown, click Backup Exec Settings > Network and Security > Disk storage lockdown settings > Disable and enter the System Logon Account credentials.

NOTE: Lockdown setting should be enabled back after running the dcscan

2. Open Command Prompt ( Run as Administrator ) and run the below command -

cd "\Program Files\veritas\Backup Exec"

crcontrol --compactoff      (Note: two dashes before compactoff)

dcscan --verify -q -H -a > crcerrors.txt 2>&1       (Note: two dashes before verify)

crcontrol --compacton       (Note: two dashes before compacton)

If the crcerrors.txt file is zero bytes, then the dcscan program did not find any corruption inside the deduplication folder.

IF DEDUPLICATION ENGINE SERVICE IS NOT RUNNING - 

The dcscan.exe program requires access to the deduplication database in order to perform its function.  If dcscan.exe is run without Deduplication Engine Service running it throws the below error : 

C:\Program Files\veritas\Backup Exec>dcscan --verify 65
Error: 67: Database: connection to database crdb at localhost:10085 failed (could not connect to server: Connection refused (0x0000274D/10061)
        Is the server running on host "localhost" and accepting
        TCP/IP connections on port 10085?
)
Error: 53: Database Manager: could not access storage database (connection actively refused).
Error: 4: Failed to run database class
Error: 4: Failed to read startup mode

Ensure the dcscan command is run with the deduplication services running.

From a command line window:
cd "\Program Files\veritas\Backup Exec"
dcscan --verify -q -H -a > crcerrors.txt 2>&1       (Note: two dashes before verify)

The output from dcscan varies according to the version of Backup Exec - the following are examples from a normal "clean" deduplication folder:

20.x

If the crcerrors.txt file is zero bytes, then the dcscan program did not find any corruption inside the deduplication folder.

21.x

CRFP(SHA) from data : cf19b1b5c8994bf24cf45f5d5fe9e8a6fb418659ea317a72b219748f0d4285f4
CRFP(MD5) from data : 470444577715f47b39f269b66560b7c8
CRFP(SHA) from data : 73852faab74c80650600f3d49a6a479eff37acf0e201efa60faa91723a849213
CRFP(MD5) from data : a5c3e42d69aca57129072dc95fd9430b
CRFP(SHA) from data : 3b4805b4d8d31c964f9a1d9f15b9edcb6e0b9930b2f85e7f32e684e70bbc0926
CRFP(MD5) from data : 7de6299666a4b38bdb041479ecdfe237
CRFP(SHA) from data : c12df97e9e3d2a17daf032a126fdbaa1fb46ee6c1c685cecf6fd0f84484dadc6
CRFP(MD5) from data : f014effc33fb39b5b43f7f409fc80efe

22.x

type of record : SO
version        : 3
flags          : 0x2
backup session : 3998301090
fptype         : 3
size           : 159
record crc     : 1515983120
data crc       : 1407723132
ctime          : 1515537744
offset         : 0
digest         : c44f245afb9e3e704c2fec51c740488d02f5bf83c556e000d71d8cb805aa5249
KMS Enc        : NO
CRC verification ok
CRFP(SHA) from data : c44f245afb9e3e704c2fec51c740488d02f5bf83c556e000d71d8cb805aa5249
CRFP(MD5) from data : 11fe4989914373b5b2b299f39fae7448
CRFP verification ok

type of record : SO
version        : 3
flags          : 0x2
backup session : 0
fptype         : 3
size           : 214
record crc     : 1568477428
data crc       : 4115540726
ctime          : 1515537753
offset         : 159
digest         : 2e589b9013214a1109a854b6e6e052cdceda75117e20c7fd0e8b802f4245aa3e
KMS Enc        : NO
CRC verification ok
CRFP(SHA) from data : 2e589b9013214a1109a854b6e6e052cdceda75117e20c7fd0e8b802f4245aa3e
CRFP(MD5) from data : 16b4078c5b0cdfb3cf1fd21c8a60cdba
CRFP verification ok

Any deviation to the above please follow the "What to do if data corruption is found" section further down.

What to do if data corruption is found

If data corruption is found in the deduplication folder, it can only be addressed using a tool available to Veritas Technical Support.  Please make sure to keep the associated crcerrors.txt file.  Having it available will shorten the time necessary to address the issue.

Applies To

Backup Exec media server with the Deduplication Option and a Deduplication Storage Folder.