Backup, Deduplication, Appending, and D2D2x Rotational Archiving

Recently Unitrends released a new series of backup appliances and this week is releasing a significant new version of its backup appliance software (Release 5.)  Release 5 includes a new D2D2x archiving system for disk-to-disk-to-disk rotational archiving as well as deduplication.

One of the major new features of the D2D2x archiving system is the ability to append archives.  Appending archives simply means that for disk-based rotational archiving the same disk or set of disks can be used as the target for archiving multiple backup sets.  In the past, appending wasn’t supported – every time a disk rotational archive was used  it would overwrite the previous archived backup set.

Another feature in release 5 is deduplication.  I’ve talked about deduplication in a lot of posts in this blog, but the most interesting one in terms of the impact of deduplication on archiving is in this post.  In essence, the post discusses why we don’t deduplicate when writing to rotational archiving but stick with data reduction via compression.

A consequence of these new features is that there is no longer a simple relationship between the size of the backup appliance and the size of the rotational archiving device.

With respect to appending, a backup appliance with 3TB of raw storage and an effective raw backup space of 2.5TB might be used to protect 1TB of protected data (note: this is a large amount of protected data for this size device and retention is going to suffer – but I’m using this to make a point.)  With appending and assuming a 2:1 compression ratio, you’re going to get at most two masters on a single-bay 1.5TB archive device (note: you can’t get three because a 1.5TB device formats to about 90% of its raw capacity.)  If you use a 4-bay  archive device, you’re going to get 8 archives of that master.

With respect to deduplication, a backup appliance with 3TB of raw storage, with an effective raw backup space of 2.5TB, and which has a data reduction ratio of 6:1 will support 15TB of backup.  Now – you’re not typically going to archive all of your backup sets at one time – but on-demand archiving of selective backup sets (yes – that’s supported as well) are going to take more archive space.

What’s the bottom line?  With release 5, you want more archiving space.