Western Digital My Book Duo DAS Review
by Ganesh T S on July 12, 2014 6:00 PM EST- Posted in
- Storage
- Western Digital
- DAS
Performance Evaluation
The WD My Book Duo ships in a RAID 0 configuration by default. We first processed our DAS test suite with the default configuration, before switching over to RAID 1 (using the WD Drive Utilities). We also tried setting up an encryption password and rerunning the benchmark numbers. The figures were quite similar (within the margins expected in repeated runs of the same benchmark), which led us to the conclusion that enabling / disabling encryption has no effect on the performance of the DAS. The full numbers are provided in the table below.
| WD My Book Duo 8 TB Performance (MBps) | ||||
| RAID 0 | RAID 1 | |||
| Read | Write | Read | Write | |
| Photos | 178.04 | 73.21 | 147.95 | 110.53 |
| Videos | 248.63 | 133.11 | 145.25 | 142.26 |
| Blu-ray Folder | 279.44 | 161.43 | 148.64 | 144.65 |
| Adobe Photoshop (Light) | 3.81 | 147.16 | 3.26 | 188.7 |
| Adobe Photoshop (Heavy) | 5.1 | 171.04 | 4.47 | 181.61 |
| Adobe After Effects | 3.71 | 47.18 | 3.1 | 65.43 |
| Adobe Illustrator | 3.8 | 76.16 | 3.23 | 94.68 |
While RAID 0, as expected, performs better for large file transfers (such as Blu-ray folders), RAID 1 wins out on some types of workloads too. On the whole, the DAS fulfills its advertised potential. Reaching up to almost 280 MBps for certain workloads, it is definitely a compelling solution for consumers looking for fast and reliable high capacity storage at a reasonable cost.
Various power consumption numbers, as well as duration for RAID rebuild (which is discussed in detail in the next section) are provided in the table below.
| WD My Book Duo 8 TB Power Consumption & RAID Rebuild | |||
| Activity | Duration | Avg. Power Consumption | |
| Idle | - | 12.41 W | |
| Disks Head Parked | 10.22 W | ||
| Disks Spun Down | - | 2.19 W | |
| Benchmark Mode (RAID 0) | - | 14.61 W | |
| Benchmark Mode (RAID 1) | - | 16.15 W | |
| RAID-1 Rebuild | 9h 47m 9s | 15.99 W | |
We find that the power consumption numbers are quite low compared to the 2big Thunderbolt 2. The presence of a 5400 rpm hard drive, coupled with some nifty firmware features help the My Book Duo score over the Desktop HDD-laden LaCie 2big Thunderbolt 2 in this aspect.
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voicequal - Saturday, July 12, 2014 - link
Why isn't the RAID 1 read performance closer to the RAID 0 read? Can't data be read from both drives in RAID 1?PEJUman - Saturday, July 12, 2014 - link
While in general I agree with your sentiment, I thought about this question before and one possible answer I came up with was to save the wear and tear on the 2nd drive. i.e. it only uses the 2nd drive when the 1st one have too much ECC.This approach matches well with the raid 1 goal of ultimate redundancy.
Ultimately, I wish more controller would expose the finer details on Raid tuning such as this option
madmilk - Sunday, July 13, 2014 - link
Not for sequential reads, because RAID 1 isn't striped. On RAID 0 you can read alternating stripes from each drive sequentially, but with RAID 1 you'd be reading the data twice.The random read scores are much closer between the two.
voicequal - Sunday, July 13, 2014 - link
I see your point that the reads won't be 100% sequential as seen by the drive heads, but if drive 1 starts reading at X and drive 2 at X+128KB, you can effectively get twice the read throughput over 256KB. Then you have to move the drive heads +128KB which does incur a performance cost.Still with a sufficiently large read block size, I would think there could be a substantial performance improvement reading from both drives in RAID 1. Does anyone know a RAID1 HW or SW controller that can do this?
DanNeely - Sunday, July 13, 2014 - link
The time spent skipping ahead is equal to the the time spend reading the area being skipped in a non-fragmented file. To double read speeds in a "mirrored" drive you'd need to have either the array controller or the driver in a software array store the file sectors as 02481357... on the first drive and 13570248... so that when reading the file the two drives are reading sequential sectors on the drive and alternating chunks of data in the file.Cerb - Sunday, July 13, 2014 - link
No, you wouldn't. You'd just need to alternate drives for reads, keeping them balanced, so that a total QD of say, 6 would be QD=2-4 on one drive, and QD=2-4 on the other. Where the file data actually gets stored shouldn't matter, only how the RAID implementation decides to read it. If the reads are sufficiently sequential, both drives should be able to stay quite busy, and get read performance around that of RAID 0.Most likely is that they didn't bother even trying that, as RAID 1 is not generally used for performance anyway.
voicequal - Sunday, July 13, 2014 - link
Your approach would make sequential reads quite fast, but at the expense of sequential writes which would be split across different areas of the drive.xfortis - Sunday, July 13, 2014 - link
This is a good question. I assume that most drives are set up in their controllers to present data sequentially from the beginning. I don't think it's very common that any type of program would ask a storage device for the second-half of a given file (at least not without having read the first half); I would think that the drive wouldn't have the capability within itself to address data beginning at an arbitrary point in a sequence of data - it always has to start at the beginning of the data(?).I think to implement this you would need to segment your data at the storage/RAID controller level, like striping but each drive has all the stripes in a RAID 1. Then at the controller level the controller would be able to take a request for data and, assuming the requested data spans at least two segments, it can produce two or more starting-addresses for the drives to read. But then your segment-size would have to be tuned to the kind of data you have (like allocation units) and also then there would be an additional level of addressing abstraction/complexity that would make any kind of data-recovery very difficult.
Everything I just said may be wrong. I'm just making assumptions and inferences because it's fun. Let's get a volunteer who has more knowledge or feels like trawling wikipedia for a while!
voicequal - Sunday, July 13, 2014 - link
Yes, I'm thinking this would be best done at the controller level. I've seen operating systems apply their own striping of sorts at the filesystem (i.e. NTFS) level. Try writing two large files simultaneously to the same hard drive. On an OS like Windows 8, the throughput is surprisingly good. This can only be achieved if the OS is smart enough to use a reasonably large "chunk" size for writing the file fragments to the disk. In this way the disk sees mostly sequential write activity despite the two concurrent write operations, while the number of file fragments tracked by the filesystem is minimized.TerdFerguson - Saturday, July 12, 2014 - link
If it can't connect directly to a router and it can't host a Plex server, I'm not interested.