Many analysts have found that on average less than 20 percent of data needs to be protected instantaneously. Therefore, 27 minutes is probably OK in this case.
What if you had a single 1TB volume? I know that it doesn’t exist, but follow the logic here. Again, at full backplane performance it would take 21.6 minutes to replicate or re-create it. It would take 9.3 hours if we went to a single tape drive, again without compression. With compression you can divide the time by three.
This is more likely. If you have 1TB, you are more likely to see it spread on 20 50GB volumes across two open midrange disk backplanes. In that case, it takes 10.8 minutes to replicate or re-create a full copy. For tape, you would place the 10 drives parallel to each other and you could get the job done in 55 minutes (divide by three for compression). That is plenty of time for most applications — not all of them, but at least most of them.
However, storage administrators frequently want to use disk as the primary source for backup and restore for a variety of reasons. This is fine, unless the cost is greater than you can afford. So, here is an alternative. Instead of doing the copy back to the same disk subsystem for $40GB (open midrange), why not use an ATA array disk for $15GB. This gives you the ability to still have your primary backup and recovery on disk, but far more cost-effectively. Expect about 20 minutes to move a terabyte if you want a full copy back. Remember, you can also use the ATA array as a primary failover volume. If you used the ATA array for a differential copy restore, the recovery time would be minutes.
Don’t forget that if you free up space on the primary expensive disk by offloading to less expensive disks, you now have more room to grow your primary applications cost-free. You may be able to defer your expensive disk acquisition costs for years by using this strategy.
An emerging technology could be thought of as continuous real and logical. It is a technology that builds on an ATA array and precludes the need for an application to replicate or restore data. It has multiple Gigabyte Ethernet interfaces and is driven by a driver and a 1U appliance. Imagine that a volume (database or file system) is defined to protect. Any write to the primary open midrange disk would also follow a RAID 1-like write to the ATA array. Any change to the primary disk has an identical change to the continuous real and logical disk. If you take a consistency checkpoint from a database, a new logical disk is created (again virtual technology).
The benefits are that you can have two to three weeks of corruption protection and instant failure protection — all for about $15 per GB. Is it fast? Assume a 1TB system. After two hours of write changes to a database, you could recover from a corruption failure in 2.9 minutes!
The economics of using expensive high-end disk storage are unsustainable in today’s economic and market climate. To meet the demands of maintaining SLAs and availability agreements on a flat budget, decision makers must approach the challenge different from what they have in the past. Albert Einstein once said, “The significant problems we face cannot be solved at the same level of thinking we were at when we created them.” We think Albert was dead on. Z