A virtual tape library, or VTL, presents storage as a tape library with tape drives for use with backup software. As most backup software works with tape libraries this means a VTL device will work with all the major software backup applications. More recent VTL’s have introduced deduplication technology for eliminating duplicate copies of repeating data so multiple copies of the same data are only stored once.
So ... when is a VTL not a VTL?
Well when it is configured with a File System Interface (FSI). This makes it appear to the backup software as Network attached storage (NAS). The following article details my experience configuring IBMs ProtecTIER Deduplication Gateway 7650G with FSI with some of the things you will not find in the IBM Redbooks.
The ProtecTIER Filesystem Interface is a relatively new feature, more commonly used on smaller appliance models and not often configured on gateway models where the greater throughput performance of the VTL is more commonly deployed. The 7650G is configured and shipped as either a VTL (with FC adapter cards) or FS (with NICs) but not both. This is something that has caught a few people out in my experience and is not easily rectified once the system is out in the field.
Unlike the appliance the storage is not integrated with the gateway model so connectivity to some backend SAN storage is required. It is recommended that SATA disks use RAID6 (6+2) and Fibre Channel disks use RAID5 (4+P to 8+P) for User data storage LUN’s and then RAID 10 for metadata LUNs (4+4 to 8+8). It is highly recommended that Fibre Channel disks be used for metadata LUNs as this stores the Hyperfactor index.
There is a sizing tool to assist with the calculations for the number of spindles, raid type, disk capacity and performance; this also requires customer information about data change rate, retention period as well as the size and frequency of backups. The sizing information is critical as you will be prompted to input these values when it comes to configuring the storage repository.
Network performance in terms of bandwidth between the ProtecTIER and the backup server is an important consideration when configuring the network port. On the ProtecTIER side the NICs come with options of either 2 x 4port GbE adapters or 2x 2port 10GbE. The ports can be bonded or linked together at a logical level to increase bandwidth over that of a single adapter. Round robin is the most straight forward option to configure as this requires no special configuration of the networks switch infrastructure and common sense dictates it is best to link ports across adapters to remove single points of failure. I discussed this with an IBM ProtecTIER consultant and was told this was suitable for performance < 500Mbps. For higher throughput speeds 802.3ad link aggregation is also supported on ProtecTIER but this must also be configured on the network switches and remember that whichever option you choose your backup server should also be configured with the same number of NICs otherwise a potential bottleneck could exist at that end.
Configuration of the shares and directories is much simpler than the ProtecTIER VTL setup as there is no requirement to configure tapes, drives, etc. we just need to create a share or shares of the required size. This makes it more straightforward to administer and manage than a VTL configuration. It is worth pointing out that using Workgroup authentication is much simpler to implement than configuring Active directory authentication which requires a detailed knowledge of an organisations AD setup.
One last point, in order for ProtecTIER’s deduplication to work it requires data to be written in large chunks from backup software application. You can present ProtecTIER file shares as NAS shares to a file sever but it will not deduplicate, which is the whole point of implementing it in the first place.
If it is a NAS solution you are looking for then a NAS storage implementation is best suited.
Should you require any further information regarding Virtual Tape Library please do not hesitate to contact us.
Neil Hulme, Technical Consultant, Celerity Limited
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