Western Digital My Book Duo DAS Reviewby Ganesh T S on July 12, 2014 6:00 PM EST
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- Western Digital
Hardware Aspects and Setup Impressions
Western Digital is no stranger to dual-disk RAID-0/-1 capable solutions, having released a USB 2.0 / Firewire 800 capable unit back in 2011 and a first-generation Thunderbolt device in 2012 along with a high-performance variant using VelociRaptor drives later in the same year. All these used software RAID, and that is where things are changing now. The My Book Duo comes with hardware RAID (and hardware encryption, if opted for). It has a USB 3.0 interface. There are two additional USB 3.0 ports in a hub configuration at the rear of the unit.
Hardware & Platform Analysis
The picture below shows the contents of the package. Bundled along with the main chassis is a 36 W power adapter and a USB 3.0 cable. The design of the chassis is very similar to what was used in previous two-bay solutions that supported replacement of disks by users (such as the My Cloud EX2).
The gallery below has some more shots of the chassis as well as some teardown pictures.
In order to provide 'daisy-chaining' capabilities, WD has put in an ASMedia ASM1074 USB 3.0 hub chip on the board. This has one upstream and four downstream ports, and supports UASP (USB Attached SCSI Protocol). We also see a JMicron JMS561 USB 3.0 to dual SATA III bridge chip on the board. In terms of layout, it is obvious that the JMS561 links to one of the downstream ports on the ASM1074. Two other downstream ports are made available on the rear side of the chassis to connect additional USB 3.0 peripherals, as needed by the user.
One of the important aspects of the My Book Duo RAID storage box is the fact that the bundled drives are WD Reds. This allows for a balanced mix of performance and power consumption, while also allowing for the unit to be connected in continuous backup mode to a PC running 24x7.
Unlike the LaCie 2big Thunderbolt 2, the WD My Book Duo doesn't have any way to configure the RAID level without connecting it to a PC and installing the WD software. At the minimum, the WD Drive Utilities software must be installed, unless the user wants to keep the default shipping RAID configuration (RAID 0). This software allows running of diagnostics (S.M.A.R.T, bad sector detection), RAID management, configuration of idle time for spinning down the disks and full erasure of the disk contents.
The WD Secure software allows setting up of a password to cryptographically protect the data on the disks. Mounting an encrypted drive without the password auto-mounts a UDF filesystem with the password unlocker utility. So, it is possible to move around an encrypted DAS without the need to install the WD Drive Utilities on the PC to which it gets attached.
In addition to these core software utilities, WD also includes a comprehensive backup suite. WD SmartWare Pro can be installed and configured to provide continuous or scheduled file backups. It can also integrate with Dropbox. For system level backup, the WD Edition of Acronis True Image is available. Readers interested in the details of various operational aspects of the WD My Book Duo can refer to the the user manual (PDF).
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voicequal - Saturday, July 12, 2014 - linkWhy 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 - linkWhile 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 - linkNot 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 - linkI 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 - linkThe 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 - linkNo, 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 - linkYour 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 - linkThis 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 - linkYes, 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 - linkIf it can't connect directly to a router and it can't host a Plex server, I'm not interested.