Ha! I'll have to settle for something less "enterprise." How about 96TB? I'm game. There aren't that many low-end storage solutions that can scale up near 100TB ranges without some serious cash and lots of racks. I'm sitting on about 2TB of data: 700G cobbled together by lvm2, and a more robust 1.4TB in a RAID5 setup backed by a 3ware 4-port 9650 RAID card. I can't bare to let drives go unused so swapping out my 4 500G drives in the RAID array for 1TB drives isn't something I'm considering even though that would double my storage to 3TB in the RAID array. Just what would I do with the other 4 500G drives? I had initially hoped that 3ware's multi-card support would allow the construction of logical arrays spread across multiple cards. That is, keep my 4 drives on the current card, purchase a 12-port 3ware, and then build a single logical array of all 16 drives. The 3ware support team said that it is possible but only using software RAID in the host. Well, duh! But what's the point of the hardware RAID?
So where does that leave us? Looking at SAS cards, that's where. SAS being the "enterprise" version of SATA; advanced features like dual ports, multi-pathing, support for large numbers of drives per adapter, etc. Two key features of SAS are of key interest. First, a single SAS card can address something in the range of 128 to 256 devices. Second, SASSATA drives are interchangable. This means you can get "enterprise" scaling (SAS), with cheaper storage (SATA). In my above example, I'd be looking at multiple sets of 16-port SATA RAID cards to get large numbers of drives going in an array. Each one of these RAID cards go for $1200-$1500 a pop. 3ware's SAS controller is $650. Yea, that's right, $650 card can support up to 128 devices!
Hold your horses because there is one other dirty secret about this gold-mine of scalability. You can't directly attach that many drives to a SAS controller. Instead, SAS relies on your storage enclosure to include an expander. This expander helps the SAS controller attach to all of these additional drives. The trouble here is that most storage enclosures with expanders included are rather pricey. Typically $3000 to $6000 - just for the enclosure; you still have to go buy your drives.
There is some light at the end of the tunnel though. First, Adaptec makes a scalable enclosure, the SANBloc S50. With 12 3.5" hot-swap bays, *and* support for daisy-chaining up to 7 S50s to a single SAS controller; we've got a big bowl of pudding here. Looking around, I see empty S50s going for around $1600. An Adaptec SAS adapter and to start with, 12 1G drives, we're looking at about $5600. All told, about $465 per TB with 1 tray and a $270 drive, $419 if you scale out to 7 trays. As drive prices go down, say $200 by end of 2008, then $395 per TB for one tray, or $349 for all 7 trays. That's downright respectable scaling and a rock-bottom price.
Now, before you choke on that initial $5600 layout, let me introduce you to the other feature of the unified SAS card from Adaptec. Rather than just having a port for external enclosures, the Adaptec RAID 51245 has 12 internal ports, and 4 external. This provides an even lower entry point by supporting up to 12 drives internally AND then any of those 7 external S50s. At the cheapest, the card will retail for around $900 and then you can add in any set of drives you like, up to 12 of them, slowly adding a drive at a time up to 12 and then scale out to external storage, all with the same card.
I don't know about you, but I'm going to go get some pudding.
1. Crude references to MTV's The State skits (Barry and Levon, Louie).
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