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This may seem a bit counter-intuitive, but I'm looking for a NAS device like the QNAP that can be direct attached to a server. The rationale here would be backup speed. I would like to backup via esata, sas, or some other fast direct attach connection, and then I would like the backup device itself to support features like automated replication over the network.

I can do this via iSCSI using QNAP devices, but the backup solution I'm interested doesn't recommend iSCSI targets (I may test this out myself to see if it's a real issue or just a recommendation).

I could also have the server do a fast backup onto local disks and then have it perform replication to a NAS, but I like the idea of inexpensive plug & play devices doing more of the work.

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What you're looking for is a bit odd. Direct attached storage devices (DASD), like SAS or ESATA enclosures are pretty common. When you talk about "replication over the network", though, you cross a boundary into something more like SAN or NAS devices.

Block-level replication of DASD could be done via software on the host OS. You don't mention your OS, but DRBD would do what you're talking about on Linux. The storage devices aren't doing the replication, though-- it's the host OS. (I'm sure there's a DRBD-alike for Windows, but I don't know of one off the top of my head. There are some rather pricey looking offerings like SteelEye Data Replication and Double-Take Availability that will probably do what you'd want on Windows.)

I suppose it would be possible to build a DASD device that contained an integrated controller to do block-level replication via a network. Since there wouldn't be contention for filesystem access with the host OS this would be feasible, but I've never heard of such a device.

File-level replication of DASD could be accomplished pretty easily by the host OS, using something like rsync, Unison, or Microsoft's DFS replication (as well as a whole host of third-party solutions).

Having a controller in the storage device itself perform file-level replication would be fairly difficult since it would have to contend for filesystem access with the host operating system. (Presumably you could use a cluster filesystem and skirt that issue, but cluster filesystems aren't commonly used on commodity operating systems.)

I would think your best bet would be some cheap DASD and a host-based replication system.

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  • Thanks Evan. I'll be more specific: I can do Hyper-V image backups to a QNAP via iSCSI. I can then make that QNAP do rsync replication over the network to another QNAP. I can also plug a USB drive into the QNAP and it'll automatically copy all the data. It's cute. My only problem is the initial backup which would have to happen over iSCSI. I'd like it to happen via eSata or SAS without adding another local disk to the process. I know it's a bit weird, but I like the idea of the host performing one backup operation, and all the other steps performed by these little devices.
    – Boden
    Commented Jan 6, 2010 at 17:35
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Yes, but it sounds like you are looking more for an external disk array than for a NAS. These devices support a variable number of drives, and can present them to the host as either a single disk (using a built in raid controller) or as multiple disks (which can be then be combined using a RAID controller built into the server or via software RAID).

Since you don't really describe the size or speed you need, I can't really recomend a specific device. But a quick google search turned up some devices that might work for you. I have not used any of these, so I'm only pointing out options and saying such devices exist.

  • AccuSTOR AS316X2 - 3U Rack mount. Takes 16 disks, SAS or SATA, and presents as JBOD via SAS.
  • NexStar - Extreme other side, small desktop size unit, 2 SATA drives, built in RAID

Again, lots of options out there, as always its a matter of features and quality versus price :)

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  • Thanks, but I'm not looking for a direct attach RAID enclosure. What I'm looking for is a bit different, and may not exist.
    – Boden
    Commented Jan 6, 2010 at 17:28
  • I'm still not 100% clear, but it sounds like you are looking for a device that has BOTH esata and network connections: esata to connect to the server and then have the device use its network connection to replicate the data to a second device. Is this what you are looking for? .....yeah, don't know anything off hand, sorry.
    – Evan
    Commented Jan 6, 2010 at 21:01
  • Correct. Thanks Evan (and Evan!). I'm testing iSCSI to see if it'll get the job done for me.
    – Boden
    Commented Jan 6, 2010 at 21:22

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