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StorCentric Drobo 8D DAS Review - 8 Bays and Thunderbolt 3

Subject: Storage
Manufacturer: Drobo

Introduction

It has been 9 years since I reviewed the DroboPro. For its time, that product was a beast of a device, with the closest to a 'set it and forget it' RAID implementation I had ever seen. It was also robust enough to shrug off any combination of power loss and pulling (failing) disks that I could throw at it. The ease of use/durability combination was a good formula for Drobo that has now lasted over a decade. The main hurdles over the years have been more on the performance side of things. The original DroboPro was indeed quicker than previous Drobos and other competing models, but competition quickly surpassed them in performance. Later Drobo models brought decent performance and capabilities for competitive prices (like the Drobo 5C), but we haven't had a worthy successor to the original DroboPro. They came close in the form of the B810 series, but those were still limited by Gigabit links. We needed the 8-bay form factor to have a larger pipe - and now we do:

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Read on for our review of the Drobo 8D

I'm showing the rear first here as that is where the most dramatic changes reside. Drobos have always had the same look up front, and the important bit for this part is pointing out the pair of Thunderbolt 3 ports at the rear. These are 40Gbps ports capable of daisy chaining a pair of 4k monitors. The Drobo 8D comes with a single 20Gbps Thunderbolt 3 cable, which is good for ~1.5 GB/s of file data throughput. While that cable provides a comfortable margin above the expected ~1.1GB/s of the 8D, display passthrough will likely require a higher bandwidth cable on either side of the 8D (if the 8D(s) are the first in the chain, which is the suggested configuration).

Also at the rear is a 2.5" SSD Accelerator Bay. Since this is a single bay with no redundancy, the SSD only functions as a read cache, helping primarily with random read performance. The functionality becomes moot with sequential workloads and higher drive counts, as the combined throughput exceeds the single SATA channel of the Accelerator Bay.

Inside the 8D is a 1.6GHz quad-core Marvell ARM CPU, which should be more than capable of moving the bits around at a reasonable speed. Also worth noting is that the large form factor of the 8-bay unit enables the use of an internal power supply. The TB3 ports are also capable of feeding 15W back to the connected system (laptop). Not enough to fast charge but perhaps enough to maintain charge level.

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The big change (aside from performance - more on that below), is an updated Drobo volume format that supports a maximum volume size of 128TB (the maximum pool supported is 256TB). Large volume sizes are important in this context as Drobo prefers to set the provisioned volume as large as possible when created so that adding drives and capacity later does not require any additional changes at the OS level. The original DroboPro had a 16TB maximum volume size and a 32TB maximum pool size, for comparison.

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The test configuration was using a set of provided Seagate Barracuda Pro 7200 RPM HDDs. 5x12TB and 3x4TB were used, and while the capacities were mixed, the Drobo fills drives at the same (absolute) rate until the smallest are full, then shifts to the remaining capacity of the larger drives. This means so long as we don't fill more than ~12TB of data (minus 1/8th for parity), we should see maximum speeds. For testing, we opted to not install a caching SSD as we wanted to get a solid and consistent read on the HDD-only performance. Caching SSD usage helps to improve random reads.

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As you can see from the above chart, Drobos have always been tough to properly benchmark. Simple 'short throw' benchmark tools don't sustain the transfer long enough to get through all of the layers of Drobo's storage stack. They tried to alleviate this with their app, dubbed 'Drobo Performance Tool', which behaves much like Iometer, but when run with the defaults, we still didn't see the same speeds as a 'real' timed file transfer.

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Speaking of real speeds, that observed 1.1GB/s comes in at exactly what was claimed during our briefed figures for the 8D, and the 448 MB/s surpassed the claimed 380MB/s. Granted we were running the 8D mostly empty during these tests, so their 8D may have been tested with more data present, possibly slowing writes a tad. These figures are a far cry from the ~80 MB/s from the original DroboPro and is a good gain on even the more recent members of the Drobo lineup.

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The Drobo 8D offered impressive speeds and larger volume support coupled with proven simplicity and robustness. These impressive features are tempered by Thunderbolt 3 support that currently only exists on Mac. A Windows driver has been promised. However, the same was discussed over multiple prior Thunderbolt models but never materialized. Another negative to some is the cost - $1299. Yes, that is cheaper than the B810 launch prices ($1699), but the 8D may be a tough sell with other Drobo 5-bay offerings running closer to $300. Some added speed and three more bays becomes a tougher sell at $1k over the 5-bay offering. Drobo does run occasional sales, typically including some HDDs with purchase. One such sale is going on today (Cyber Monday), where an 8D purchase will come with a 250GB Samsung 860 EVO SSD, which is a nice model to use as a hot data cache.

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Performance and ease of use are solid, but the high cost and lack of Windows support make the 8D a tough sell for some.


November 27, 2018 | 01:36 PM - Posted by Donkey (not verified)

Assuming DAS means Direct Attached Storage, what's the point or benefit of it over a more standard NAS ?

November 27, 2018 | 02:43 PM - Posted by Rick Farris (not verified)

Traditionally a DAS would be used to supply OS images - IOW fast enough to run a virtual OS providing backing memory for VMWare or some such. Pretty unusual for the Mac world.

November 27, 2018 | 05:00 PM - Posted by jgstew

The max speed of a NAS is limited by the throughput and added latency overhead of Ethernet. DAS or Direct Attached Storage generally has higher maximum sequential throughput, as well as much better latency.

One of the drawbacks of DAS over NAS is direct storage can only be enumerated by a single computer at a time, and that computer must act as a file share in order to make the storage available to other computers on the network.

DAS is preferred in uses cases like Video editing, where you might need to work with a very large set of source files on a single computer that would not fit on that computer's internal storage, but there are other uses as well.

iSCSI is a technology that allows Network Storage to act more like Direct Storage, for both better and worse.

That said, I'd love to see this exact same Drobo but with in a 10Gig+ NAS config.

December 3, 2018 | 04:01 PM - Posted by RyanSmith (not verified)

Where did you find that Drobo performance tool app? I've never seen that before.

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