A thin provisioned filer is a happy filer – especially from a data protection standpoint. In this context a thin provisioned filer is a filer that has plenty of free space due to older unused files moved somewhere else. Unfortunately, such filers can be quite uncommon and create a number of management challenges for their owners.
When filers get full, the first thing administrators tend to do is to look where they can reclaim space. The most obvious place to look is snapshots, as a significant number of snapshots can take up a large percentage of a filer. This is especially true in NetApp filers where the snapshot data shares the same volume with the primary data. Having snapshot history and primary data in the same volume is one of the reasons NetApp filers can create as many snapshots as they do without any performance impact. However, it’s also what makes those same snapshots vulnerable to administrators looking to save some space. All they have to do is delete a few snapshots and they have gained a significant amount of space in the production file system.
If the snapshots are being deleted prematurely in order to make room for primary data, then both historical data and future data is at an increased risk due to there not being enough available space to store the amount of history that you would like. If your requirements are to have 30 days of user-browsable snapshots, but you only have space for 15 days of snapshots, you will not be able to meet your data protection requirements.
Another risky situation is the combination of a full Netapp filer, followed by the use of deduplication combined with SnapMirror to Tape. The purpose of SnapMirror to Tape is to facilitate the quick restore of the entire volume, but deduplicated data is rehydrated when it is sent to tape. In order for the restore to work, there needs to be enough room for the rehydrated data as it will be written to disk and then deduplicated. If there is not enough spare room to write the rehydrated data to disk, a restore from SnapMirror to Tape will not be possible. If SnapMirror to Tape is the customer’s only backup method, they will be forced to buy a larger filer in order to facilitate the restore.
Another advantage of a thin provisioned filer is that backups are faster and take up less space. This is important, since for every 1 GB of primary storage there is 20 GB in secondary storage. Therefore clearing out 1 TB of extraneous data from your filer clears up 20 TB of space in your backup system. That’s 20 TB that you do not have to store the backup system, 20 TB that you do not have to transfer across the network, and 20 TB for which you do not have to run NDMP. Faster backups also tend to be more successful and are therefore more valuable to your organization.
One of the ways to create a thin provisioned filer is to free up space using an object storage system to move lesser-used files off of the filer. Storing them in object storage costs less and frees up space for snapshots, deduplication, and over provisioned applications. This frees up space in your filer and the backup system, as files stored in the object storage environment are automatically protected.
NetApp filers work best when they have a buffer of free space available to them. Customers can keep the number of snapshots that their data protection requirements demand. They can also use products like SnapMirror to Tape without any negative ramifications during a restore. Finally, backups run smoother and cost less money when a filer is thin provisioned. Customers with these filers should examine the idea of moving older data off of the filer and onto a less-expensive storage system, such as an object storage system. It just makes sense.
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