TCO issues in disk technologies part 2: ROI

Computer Technology Review, August, 2004 by Jim McKinstry

Last month's article in CTR about Total Cost of Ownership discussed how to determine the costs of a storage solution. The TCO of a storage solution is important to know, as it can be much higher than anticipated; but it can usually be offset by a Return on Investment. ROI is how much profit or cost savings are realized over the life of the solution and can be very aggressive for a storage solution.

Straightforward Replacement

Many storage solutions purchased today are replacing systems that are no longer covered by the initial warranty. Monthly maintenance costs for old storage can easily exceed a lease payment of a new purchase. For example, if the maintenance cost for an old system is $3,000 and it costs $2,500/month for a three-year lease to replace the system with a new system, that $500 difference goes directly to the "profit" column. Sometimes, just replacing older storage with newer, less expensive solutions will decrease the monthly cost to operate and provide an immediate ROI for that application.

Performance: With a replacement storage system, it is almost guaranteed that there will be better performance with the new solution. Storage solutions, a few years ago, were based on 1Gb Fibre Channel. Today's solutions are mostly 2Gb (i.e. double the potential bandwidth--MB/sec). Storage controllers are also becoming faster in processing the number of transactions (i.e., I/Os per second). Most Fibre Channel disk drives are now spinning at 15,000 rpm. This faster performance allows databases to process more data in a shorter period of time. Disk-bound applications will benefit from the faster storage devices. For example, using a storage device purchased today versus a storage device purchased three years ago, streaming video applications deliver the content much faster, allowing for more content to be transferred; an application that generates revenue based on the number of transactions processed (i.e., credit card adjudication systems) will process far more requests per minute with controllers and disks able to deliver more I/Os per second.

"Advanced" Replacement

Many older storage solutions were purchased when "premium features" (snapshot, remote replication, etc.) were new and cost prohibitive to implement. With recent market conditions bringing about aggressive pricing, an outdated "basic" storage system can now be replaced with a more robust, feature-rich solution where ROI can be realized in many areas.

Snapshot

Replacing a "bare bones" storage system with a solution that has snapshot technology can dramatically increase the ROI of the purchase. Since the new storage system is likely to perform twice as fast as the existing solution, implementing snapshots on top of the new storage will not negatively affect performance. Here are a few examples of how the snapshot feature can increase ROI:

Backup: Snapshot technology can be used to essentially eliminate a backup window. There are two methods to performing a backup: cold and hot. A cold backup is when an application is taken off line, which means there's no user access to the data, and the data is backed up. A hot backup is when the application remains online and user access is retained while the backup is performed.

A cold backup is usually the optimal solution for those applications that can tolerate multi-hour downtime to perform the backup. Some applications that used to be backed up cold have now grown so large that the backup cannot be completed during the allotted window. If a cold backup is still desired, implementing a snapshot allows the application to be taken offline, a point-in-time "snapshot" of the data is taken, and within a matter of seconds, the application is brought online. The snapshot can then be mounted back onto the application server, or mounted directly to the backup server, and backed up. Total downtime for the application is the time it takes to stop the application to perform the snapshot and then restart the application.

Since many applications must perform with zero downtime, a hot backup must be used. A hot backup is when the data is quiesced (i.e., Oracle database is put into hot backup mode) and backed up in that state. While the data is quiesced, the application usually experiences a performance penalty.

When first implemented, this lag in performance may have been acceptable. As the application data grows, however, the length of time needed to perform the backup also increases--which means the length of time the data is quiesced is longer. The longer an active application's data is suspended, the longer it takes to reactivate the data, which also impacts performance. If a snapshot is implemented, the backup would consist of suspending access to the data (typically, seconds or a few minutes), taking a snapshot (seconds) and releasing the data (seconds). As with a cold backup, the snapshot can be mounted to the application server or backup server and backed up.

For either type of backup, implementing a snapshot will practically eliminate the backup window for the application. This will allow the application to stay online and running optimally for the maximum amount of time, which allows for more transactions to be processed in a day. If a value can be assigned to a transaction, then this can be used as part of the ROI equation.