LTO1 backup surprise

Sometimes, it’s nice to be pleasantly surprised:

Yip. I’m averaging 40MB/sec on a backup heading to LTO1 media from my NetBackup media server. The data is arriving from another Sun box over the network, but that’s not important. What is relevant is the drive: an IBM LTO2 unit. It sure is nice to see these new drives extract a little more performance from my existing pool of LTO1 tapes. And yes, I’m obviously getting excellent (probably close to 2:1) compression of the data by the drive. So “real” throughput to the tape is probably 20MB/s. Which is just fantastic.

I highly recommend the IBM LTO2 drives, BTW. They’ve been nearly flawless for us over the last 6 months in our L700. The local STK rep was going to spec HP drives, but I’m glad I explicitly requested IBM.

A minor clarification, and a major point regarding HP vs. IBM LTO drives.

1> An LTO-2 drive using LTO-1 media will run at LTO-1 speed, which is 15MB/s native. That’s what’s going to the drive, period. With 40MB/s from NBU, you’re getting a fairly impressive 2.7:1 (approx) compression ratio. That all happens before you hit the actual tape drive, in the magic compression part of the drive controller (on the drive). Nice, very nice.

2> HP and IBM have sort of off-setting goodness in their LTO-2 implementations. IBM claims (and nobody refutes it, so it’s probably accurate) 35MB/s native data rate for their LTO-2. HP’s spec says 30MB/s, exactly double LTO-1 (both HP and IBM were 15MB/s on LTO-1). Advantage IBM. But wait, there’s more…

HP’s LTOs (all) have a neat feature called “data rate matching”. This comes into play when you are not able to sustain the full data rate needed to keep one of these fast drives streaming. This happens a lot with network backups, although Gig-E hides a multitude of sins in this regard. HP’s data rate matching slows the drive, in increments so fine-grained as to be effectively continuous, down to quarter speed at a minimum, to allow the drive to continue to stream even in the face of a slow data feed from a backup.

Without this feature, IBM drives end up stopping and starting a lot, for slow backups. This puts lots of extra miles on the drive and media both, litterally wearing them out in half or a quarter their expected lifespan in extreme cases. HP’s data rate matching prevents this in all but the worst cases, and reduces it even for those.
Advantage HP.

STK’s engineering has determined that the HP advantage is great enough that they’ve declared HP to be their “Preferred LTO vendor”, so HP LTO is the default in their configurator (so I’ve heard). That’s why the STK guy recommended HP.

For people in your situation, with decent network and backup client performance that can feed these fast, hungry drives their bytes, IBM is not a bad choice. But lots of my customers are in the other camp, with lots of clients still on 10/100 links or with slow filesystems that Gig-E can’t help. For them, HP has a much better story.

My $.02, for what it’s worth. –bmr

VMUNIX Blues

LTO1 backup surprise

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