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Sizing your disk backup and deduplication system to avoid future missteps

Bill Andrews | April 29, 2013
Correctly sizing a disk backup with deduplication to meet your current and future needs is an important part of your data protection strategy. If you ask the right questions upfront and analyze each aspect of your environment that impacts backup requirements, you can avoid the consequences of buying an undersize system that quickly exceeds capacity.

* Rotation. Your backup rotation will also impact the size of the disk-based backup with deduplication system you need. If you are doing rolling full backups each night, then you need a larger system than if you are doing incremental backups on files during the week and then a weekend full backup. Rotation schemes are usually:

Database and email

Full backup on Monday, Tuesday, Wednesday, Thursday, weekend

File data

Incrementals forever or optimized synthetics -- this copies only changed files each night, and there is no weekend full

Incrementals -- Copies changed files each night, full backup of all files on the weekend

Differentials -- Copies files each night that have changed since the last full backup, full backup of all files on the weekend

Rolling fulls -- Breaks total full backup into a subset and backs up a portion of the full backup each night (e.g., if the full backup is 30TB, then back up 10TB each night and keep rotating on a three-day schedule)

Because the backup rotation scheme you use changes how much data is being sent to the disk-based backup with deduplication system, this also impacts the system size you require.

* Cross protection. Two scenarios:

Sizing Scenario 1: You are backing up data at Site A and replicating to Site B for disaster recovery. For example, if Site A is 10TB and Site B is just for disaster recovery, then a system that can handle 10TB at Site A and 10TB at Site B is required.

Sizing Scenario 2: However, if backup data is kept at both Site A (e.g., 10TB) and at Site B (e.g., 6TB), and the data from Site A is being replicated to Site B while the data from Site B is being cross-replicated to Site A, then a larger system on both sides is required.

Bottom line for sizing a system

In summary, dozens of possible scenarios impact the sizing of a system, including:

How much data is in your full backup? What percentage of the data is compressed (including media files), encrypted, database, unstructured?

What is the required retention period in weeks/months on-site?

What is the required retention period in weeks/months off-site?

What is the nightly backup rotation?

Is data being replicated one way only or backed up from multiple sites and cross-replicated?

Other considerations unique to your environment

When working with a vendor, ensure it offers a tool that allows it to calculate the exact size of the system you need based on all of the above.

It is very common to see an organization acquire a disk backup with deduplication system and, in a few short months, have it fill up because the system was undersize, retention was longer, the rotation scheme put more data into the system, the deduplication method had a low deduplication ratio, or the data types were such that they could not deduplicate well.


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