Snap Pool Size Planning• Factors to consider

Number of snapshots planned for the master volume. Size of the master volume Amount of changed data written to the master volume

between snaps Specifically how much data is either new or modified

Will the snapshot volumes be mounted for write access? If so, how much unique data will on average be written to

each snapshot volume? • Based on this information, a customer can

estimate how much snap pool space is needed for a master volume, using the general equation

( (amount unique data written to master volume per each snapshot * # snapshots)+ (amount unique data written to each mounted snapshot volume * # snapshots written)

+ snapshot function reserve space (plan on 600 MB) )* 1.25 (safety factor)

Snap Pool Size Planning - Example• Master volume = 100GB• Average 10% change rate = 10GB• Keep 5 snapshots all mounted• Average 2GB changed data on mounted snapshots

( (amount unique data written to master volume per each snapshot * # snapshots)+ (amount unique data written to each mounted snapshot volume * # snapshots written)

+ snapshot function reserve space (plan on 600 MB) )* 1.25 (safety factor)

((10GB * 5) + (2GB *5) + .6GB) * 1.25

((50GB) + (10GB) + .6GB) * 1.25

75.75 GB

((60.6GB) * 1.25 If you have multiple volumes associated with the snap pool you need to calculate those individually

and add them to the snap pool space.

AssuredSnap Resources – Data• A snapshot may consume up to 200% of the size

of the master The preserved data is tracked by one top level page table The write data is tracked by a different top level page

table

Since the preserved and write data is tracked separately, if every block is over-written on the master volume and every

block is over written on the snapshot, the snapshot will consume 200% of the size of the master volume