Archive for June 2nd, 2008
Celerra SavVol-Maintaining Rolling Checkpoints
Whether its common knowledge or not I thought it would be worth sharing tips to controlling sporadic SavVol growth. For those that arent privy, SavVol is an area of a celerra volume where point-in-time blocks of data of a filesystem are kept. Snapsure, which is the enabler for checkpoints on the celerra, maintains a copy on first modify canon. Now without getting too in depth, as there are 70 page documents written on this process alone, lets assume you have previous experience with the Celerra and an understanding of Snapsure more importantly.
So administratively, space conservation as it relates to checkpoints doesnt have to be a manual task. If you primary concern is to maintain rolling checkpoints operating within a set amount of disk space then this process may be worth entertaining. To achieve this, we will specify a high water mark of zero percent during the creation of the checkpoint. This instructs SS not to extend the SavVol if the checkpoint reaches beyond the capacity of the filesystem. Rather, the oldest checkpoint is deleted and the freed space is used to keep the most recent checkpoint engaged. Each time a checkpoint needs space to complete, this process is repeated.
As stated, this method deletes the oldest checkpoint to keep the most recent active. So if any of that latter checkpoint data is needed then the following must be done:
- Backup the checkpoint to tape
- Extend SavVol to keep the checkpoint from being deleted
Remember at any time you can verify the SavVol space by running fs_ckpt “fs_name” -list command.
