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OWC Thunderbay 6: RAID-5 Performance

OWC Thunderbay 6

Configurations up to 84TB. Available in RAID edition (includes SoftRAID XT) or standard edition.

The OWC Thunderbay 6 houses six hard drives in one enclosure.

There are some bandwidth limits to the hard drives; see the comments on the RAID-0 results page.

Testing details

Six Toshiba 14TB hard drives were used. These are very fast state of the art hard drives, the fastest MPG has yet tested as of early 2019.

Tested using the run-area-test of diglloydTools Disktester as follows:
disktester run-area-test --iterations 5 --xfer 768M --test-size 8G

Test mule was the 2018 Mac mini. The tests were run with all six drives in a single OWC Thunderbay 6 enclosure, and again with 3 drives in two OWC Thunderbay 6 enclosures, each on a different Thunderbolt 3 bus.

Test results, RAID-5

Like all hard drives, the outer tracks are much faster than the inner tracks; see Drive Capacity and Speed. Hence the speed across capacity steadily declines as expected behavior.

Single Thunderbay 6

Using RAID-5 is actually more demanding of bandwidth in this sense: to write a terabyte of data onto a RAID-5 volume, the bandwidth required actually 1/6 higher, or about 1.167 terabytes—that’s the parity information required for RAID-5. Hence RAID-5 performance

The peak speed with a single OWC Thunderbay 6 enclosure tests at 882 MB/sec for writes and 953 MB/sec for reads (RAID-5). The write speed seems a little lower than expected but it might have to do with bandwidth contention or parity computation overhead. The speeds are maintained out to about 60% of capacity, which means the first 42TB of the 70TB volume. The remaining 40% of volume capacity suffers the inevitable dropoff from declining hard drive speed (any/all hard drives).

Perspective check: even with a single enclosure and nearly 100% of capacity, the RAID-5 speed exceeds the sustained transfer performance of a fast SATA SSD (about 550 MB/sec)!

Assuming a peak speed of 260 MB/sec for the Toshiba 14TB drives, the maximum potential read speed should be about 380 + 380 + 260 = ~1020 MB/sec (five drives at peak speed subject to bandwidth limit of ~380 MB/sec per pair of drives). Actual speed of ~955 MB/sec is very close to that, and considering that RAID-5 is involved and that drives might really be in the range of 240 to 260 MB/sec in this usage scenario, the speed is impressively good.

With dual OWC Thunderbay 6 enclosures, the bandwidth limits disappear; speed is about 21% faster for reads and 30% faster for writes when empty (0% mark). That differential narrows as the capacity utilization increases until there is little practical difference at about the 60% capacity mark (42TB of the 70TB capacity). Those looking for really fast RAID-5 (or RAID-0) will want to partition off up to the first 40% or so of the capacity as a fast volume, and use dual enclosures (or dual OWC Thunderbay 4 units).

But wait, there is another way to look at this behavior that still ends up making the Thunderbay 6 a better choice, with just 5 drives.

Vertical scale is MB/sec. Horizontal scale shows percentage of volume capacity, e.g., 50% of an 84TB RAID-0 stripe is 42TB of the capacity.


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