Veeam B&R 5: Block Size Optimization and Reversed Incremental or Synthetic Full

By admin, December 20, 2010 12:31

Saw these two piece of useful information on Veeam’s forum today, mostly contributed by Tom:

Block Size Optimization

In the job properties, on the “Backup Destination” if you hit “Advanced” and then select the “Storage” tab with V5 you can now select to optimize for Local disk, LAN target, and WAN target. What this is really doing is setting the “block size” of the VBK. Previous version of Veeam always used 1MB blocks, which is now the equivalent of the “Local disk” option. LAN target uses 512KB blocks, and WAN target uses 256KB blocks. The smaller blocks sizes typically mean that incrementals are smaller and thus less data is transferred over the LAN or WAN at the cost of some CPU. Because we push our backups across sites we always use the WAN target settings.


Reversed Incremental or Synthetic Full

As a general rule, reverse incrementals are going to use the least amount of space on disk, but the most amount on tape, while the reverse is true of forward incrementals, they will use more disk space, but significantly less tape space. The only exception might be if you have a fairly small retention period.

Assume you have a 100GB full backup with 10GB of changes a day, here’s how the space would break down assuming 4 weeks retention:

Reverse Incremental:
Disk — 100GB Full + 280GB (10GB/day * 28 days) of reverse incrementals = 380GB
Tape — 100GB VBK copied to tape every day * 28 days = 2.8TB

Forward Incremental w/Synthetic Full:
Disk — 400GB (100GB Full * 1 per week) + 240GB (10GB/day incrementals * 24 days) = 640GB
Tape — Same as disk, since you simply copy the full or incremental to tape every day = 640GB

So, the Forward Incremental/Synthetic option in this scenario would use ~70% more disk space, but less than 25% of the tape space. If you’re planning to keep only a short period of disks on retention and use tape for long term storage then forward incrementals will save space, but that’s about the only scenario where it will save space. For the best space savings with on disk retention, reverse incremental are the way to go, but at the cost of a large amount of tape space.


Personally I prefer reversed incremental because my main strategy is to get a full working backup to tape every night without the need to merge increments when in an emergency need to get my files back from tape.