I've got a first-gen Drobo, the one that was only USB. I got it used for $150.
With that disclaimer out of the way, you do need to understand that you are not paying for a simple RAID array. There's plenty of ways you can get a RAID0+1 setup, and if that's what you want, you can do it fairly cheap. You are also not paying for the interface ... Thunderbolt is not what's driving up the cost here. Drobo's new releases area always on the high-end, and then they reduce the prices on the older models. (The first-gen Drobo is the only one to have been officially retired, as far as I know. Maybe one of the other Pro models, too.)
What you pay for with Drobo is their tech. You're paying to not have to find matched drives. You're paying to not have to configure the array yourself. You're paying to have a zero-config kind of setup. You're paying for the ability to just remove a drive and add a bigger one anytime you need more space. You're paying for the ability to not have to really know much of anything about computers to get it up and running. And you're paying for the ability to simply remove a bad drive and replace it. These are all things any other RAID or NAS can't give you. You're paying for convenience, and Drobo is VERY convenient.
What you are not paying for is the speed of a RAID1 configuration. You're not paying for a foolproof backup system. You're not paying for an open system. And you're not paying for a device that will never fail. Sadly, Drobo was very unclear about a lot of this in their marketing. I think if they had been more upfront about the drawbacks and not have positioned it as a panacea, they'd have done a lot better. I personally think you should do your homework before buying anything, but Drobo is largely at fault for making it seem like a "perfect" solution.
The first-gen Drobo I have is dog-slow. It's even worse if I dare try to pull data off my Time Capsule over wireless and load it onto the Drobo without a step in-between. I've since learned not to do that. It's very slow even over USB when writing data, but that's because it's laying out the data with it's algorithm as it writes, and that's messy. Supposedly, newer boxes have faster processors and more cache, so I'm sure as I upgrade, I'll be more happy with the speed. I'll likely get a Gen2 (as soon as I can find one for about the same $150 I paid) and sell this one off soon, and I'll make sure anyone that buys it is aware of the issues. The nice thing is I can just pull the drives from this Drobo, stick them in the new one, and I'm off to the races. You can't do that with any other RAID solution.
The biggest problem I had (which I figured out on my own) is that it's unclear how to handle shutting down these older ones when you don't have Dashboard available. In my case, I made the mistake of hooking it up to my Time Capsule and using it like a NAS. But that was a mistake, and moving it back to the Mac had me corrupt some of the data, because I couldn't shut it down properly. A quick pass with DiskWarrior resolved the problem, but it took the better part of a day to figure out why it happened.
Suffice it to say that I think Drobo could have better handled some of the inherent problems with their solution by being more up-front about it. That said, I have no real issues with their pricing other than just not being able to afford it, but there's a lot of things I can't afford. It doesn't mean it's not priced fairly. They should not price their devices the same as devices that do less, and expecting them to is unreasonable. Nothing competes with Drobo in the areas they prioritize.
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For the record, the mSATA SSD should only improve READ speeds on data loaded into that drive automatically by the Drobo (data-aware tiering). I don't believe it's being used as a write-cache at all. I hope I'm wrong about that, however.
With that disclaimer out of the way, you do need to understand that you are not paying for a simple RAID array. There's plenty of ways you can get a RAID0+1 setup, and if that's what you want, you can do it fairly cheap. You are also not paying for the interface ... Thunderbolt is not what's driving up the cost here. Drobo's new releases area always on the high-end, and then they reduce the prices on the older models. (The first-gen Drobo is the only one to have been officially retired, as far as I know. Maybe one of the other Pro models, too.)
What you pay for with Drobo is their tech. You're paying to not have to find matched drives. You're paying to not have to configure the array yourself. You're paying to have a zero-config kind of setup. You're paying for the ability to just remove a drive and add a bigger one anytime you need more space. You're paying for the ability to not have to really know much of anything about computers to get it up and running. And you're paying for the ability to simply remove a bad drive and replace it. These are all things any other RAID or NAS can't give you. You're paying for convenience, and Drobo is VERY convenient.
What you are not paying for is the speed of a RAID1 configuration. You're not paying for a foolproof backup system. You're not paying for an open system. And you're not paying for a device that will never fail. Sadly, Drobo was very unclear about a lot of this in their marketing. I think if they had been more upfront about the drawbacks and not have positioned it as a panacea, they'd have done a lot better. I personally think you should do your homework before buying anything, but Drobo is largely at fault for making it seem like a "perfect" solution.
The first-gen Drobo I have is dog-slow. It's even worse if I dare try to pull data off my Time Capsule over wireless and load it onto the Drobo without a step in-between. I've since learned not to do that. It's very slow even over USB when writing data, but that's because it's laying out the data with it's algorithm as it writes, and that's messy. Supposedly, newer boxes have faster processors and more cache, so I'm sure as I upgrade, I'll be more happy with the speed. I'll likely get a Gen2 (as soon as I can find one for about the same $150 I paid) and sell this one off soon, and I'll make sure anyone that buys it is aware of the issues. The nice thing is I can just pull the drives from this Drobo, stick them in the new one, and I'm off to the races. You can't do that with any other RAID solution.
The biggest problem I had (which I figured out on my own) is that it's unclear how to handle shutting down these older ones when you don't have Dashboard available. In my case, I made the mistake of hooking it up to my Time Capsule and using it like a NAS. But that was a mistake, and moving it back to the Mac had me corrupt some of the data, because I couldn't shut it down properly. A quick pass with DiskWarrior resolved the problem, but it took the better part of a day to figure out why it happened.
Suffice it to say that I think Drobo could have better handled some of the inherent problems with their solution by being more up-front about it. That said, I have no real issues with their pricing other than just not being able to afford it, but there's a lot of things I can't afford. It doesn't mean it's not priced fairly. They should not price their devices the same as devices that do less, and expecting them to is unreasonable. Nothing competes with Drobo in the areas they prioritize.
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I'm very excited about the Drobo 5D.
But I can't make use of it yet because both my Macs do not have Thunderbolt. The ability to add a mSATA SSD to it will also improve the speed of the machine.
For the record, the mSATA SSD should only improve READ speeds on data loaded into that drive automatically by the Drobo (data-aware tiering). I don't believe it's being used as a write-cache at all. I hope I'm wrong about that, however.