Disk vs. tape is not a new argument, but over time it takes on different permutations, especially as disk-based backup in its various forms gains popularity and new technologies get introduced like data deduplication that bring some of the economics of disk closer to those of tape.
One theme I’ve heard cropping up in this discussion among high-end vendors lately is the idea of people in large enterprises deploying vast amounts of disk for backup, then realizing the cost inefficiencies, and space and power requirements of disk, and finally running back to tape either alongside or as a replacement for disk.
This back-and-forth popped up again in post written by IBM’s Tony Pearson in response to a post written by Hitachi Data Systems’ Hu Yoshida. Yoshida’s post referred to a conversation with a storage admin at SNW who said his robotic tape libraries were actually drawing more power than his enterprise VTL.
This idea makes Pearson sputter:
I am not disputing [the] approach. It is possible that [the user] is using a poorly written backup program, taking full backups every day, to an older non-IBM tape library, in a manner that causes no end of activity to the poor tape robotics inside. But rather than changing over to a VTL, perhaps Mark might be better off investigating the use of IBM Tivoli Storage Manager, using progressive backup techniques, appropriate policies, parameters and settings, to a more energy-efficient IBM tape library. In well tuned backup workloads, the robotics are not very busy. The robot mounts the tape, and then the backup runs for a long time filling up that tape, all the meanwhile the robot is idle waiting for another request.
The weird thing is, I’ve heard plenty of vendors debating this of their own accord, usually taking sides along product lines with tape-centric vendors taking the position Pearson did, and vendors who sell disk for secondary storage taking the opposite view.
But I’m curious. I’m sure there’s some middle ground where the advantages and disadvantages just depend on personal preferences. But might there really be a trend here? Are users finding problems with disk-based systems and re-integrating tape? How many organizations really even left tape totally behind to begin with? And how do new data reduction/power reduction technologies change the equation? One thing not addressed by either Pearson or Yoshida’s post is where MAID might come into this argument, as well as the potential combination of MAID and dedupe.