Coherency Check

In this article you will find an in-depth analysis to better understand what the Coherency Check is and how it works.

Zextras Backup takes care of your data, with costantly updated copies of them, but sometimes you can experience system failures or other situations that can corrupt your backup data. That’s where coherency check comes to help.

Coherency Check, in fact, is an element of Zextras Backup that performs a deeper check of a Backup Path than the one done by the SmartScan. Coherency check executes an in-depth check of all the metadata and BLOBs in the backup path. SmartScan, on the other hand, works incrementally, checking only those items that have been modified since last scan.

HOW IT WORKS

The question, now, is: how it works? And when I should use it?

As we wrote above, Coherency Check verifies the integrity of all metadata in the backup path and of the related BLOBs. It can happen that, during the check, some errors are found. In this case, if you run the test using the fixBackup option, you will obtain that any orphaned or corrupted metadata or BLOB is moved to a chosen directory inside the backup path itself.

The next question we made, was not only “how” but “when” you should do a Coherency Check. Here are some main situations where to use it:

  • For sure, at regular interval periods, as a normal check, to be sure that everything works fine.
  • If you experienced a system crash. After that one or more mailbox nodes may be shut down anomalously and as a result of which a loss or corruption of saved data.
  • If you find any malfunctioning or failure on your storage device or filesystem containing the backup. In this case a coherency check is important not only to be sure to have the access to data now and in the future, but mainly to check that every file and piece of data is ok.

Pay attention that the Coherency Check is highly I/O consuming, so make sure to run it only during off-peak periods.

Should the SmartScan detect a possible item corruption, a Coherency Check will be started automatically.

RUN A COHERENCY CHECK

The Coherency check can only be use via CLI since it is not available via admin zimlet. To perform it, you have to use the following command:

zxsuite backup doCoherencyCheck [backup_path]

For a complete and updated list of available parameters to the above command line you can refer to official Zextras Suite Documentation page

In addition, you can choose to add some other optional parameters to this command, such as:

  • accounts – selecting specific account names or IDs
  • checkZimbra – with this option enabled you are going to check also the coherency with data running on Zimbra.
  • fixBackup – choose this option if you want to move corrupted or orphaned files to a specific directory inside the backup path as we already saw before.
  • notifications – Enable this option if you want to receive a message to a selected mail address when the job will be finished.

LAST CHECK

If you want to check the status of a running scan, you can do that using the following command line:

zxsuite backup monitor [operation_uuid]

You can eventually add, as an optional parameter, also the operation_host.

Technical writer at Zextras. Linux and technology enthusiast. He describes himself as an atypical and polyhedric IT expert, thanks to a creative and open minded attitude, and to the experience gained over time as an IT technician, system engineer and developer.

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