Is your RAID lying to your app? - I/O with Mark & Hal

Computer Technology Review, Sept, 2002 by Mark Ferelli, Hal Glatzer

MARK: Have you noticed the virtualization of the storage industry, especially when it comes to HDD RAIDS?

HAL: What's "virtual" about a disk drive?

MARK: I'm talking about making the most of storage resources-disk resources, that is.

HAL: Why? Is there a shortage of storage space? Drives are cheap.

MARK: Not a shortage. Quite the opposite. Many end-users are making use of only 30-40% of their RAID disk capacities.

HAL: There's no technical. reason for that, is there? I mean, unless managers are setting capacity aside for redundancy or automatic backups, and just never getting around to recording those sectors. Are they doing that?

MARK: In some cases, yeah, I guess they could be. But for the most part, it's bad. management.

HAL: Whoa! Don't scare off our readers! They don't want to hear that they might be bad managers.

MARK: I don't think that'll be news to a lot of them! Storage management is a growth area-

HAL: And they've got to grow with it.

MARK: We've talked before about the problems you run into when you over-specify products. Nothing exemplifies that better than HDD capacity. You've got managers ordering extra capacity when they're using only 3040% of what they already have.

HAL: I heard you give out those numbers before. Where did they come from?

MARK: Ed Broderick, one of the analysts at the Robert Frances Group, said that the cost of managing disk storage today is approximately four to 10 times the acquisition cost of a RAID subsystem, and that only 30-40% of that capacity is actually used.

HAL: Assuming that's true, what does that mean for storage managers?

MARK: At the StorageWorld conference, held in August, StorageTek unveiled its latest shared-virtual array product, which it claims will move utilization up to about 80%.

HAL: But I still don't see any underlying reason for anxiety. Efficiency is practically automated, these days. When I check my own disk drives every couple of months I get rid of unnecessary files, I run optimization utilities, like a defragmenter, and generally open up more capacity, There are plenty of equivalent tools for managing big RAIDS.

MARK: The tools are there. But are they being used?

HAL: Well, if not-why not?

MARK: A matter of limited time, I think. Does that manager really have the time to delete old email, defrag drives, and so on?

HAL: It's in the job description, I'm sure.

MARK: But he or she may not have final say over what gets saved and what doesn't. Would you delegate to someone else the responsibility for deciding which of your own emails was important and which wasn't?

HAL: Hmmm, you may be right, there. I don't think people in other departments want to give up the final say-so when it comes to files that they created or may want to refer to sometime in the future.

MARK: So they go to IT, and say, "We need X-amount of capacity." And that's where virtualization comes in. It lets managers maximize their existing disk utilization. It also eases the pressure on IT budgets, which will stretch further if managers don't have to keep buying new equipment.

HAL: I still don't see how it all works, though.

MARK: Okay. Let's say an application needs access to 2GB to run, but it may not need all of that capacity right away when it launches. So, a virtualization scheme tells the app: "You've got two gigs from the start," which isn't really true. You're sort-of lying to the app. As the app demands more storage, it gets more, but only in increments. That allows IT managers to pay as they go and not have to buy those extra 2GB just for that app.

HAL: I see. Virtualization gives an app what it needs at any given moment in time, rather than dedicating a big block of disk space to it, whether. it needs that space or not. Let's see if our readers- and they're all good managers, of course-

MARK: Of course! Let's see if they're using a virtualization strategy already. If you are, let me know, at mark_ferelli@wwpi.com.

HAL: And if you don't quite get the point of virtualization, or you think it's still just a buzzword to scare managers into buying new software, email me at hal_glatzer@wwpi.com.