Dot Hill NDA Material 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)

Dot Hill NDA Material 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) * 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.

Dot Hill NDA Material 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