2/27/2009: Revisions from vendor feedback
If you have or are thinking of buying a BYOD (Bring Your Own Drive) NAS, you might think that you can throw any ol' drive that can fit into it. But NAS vendors spend a lot of time and effort to come up with lists of qualified or approved drives for their products.
But these lists don't include every possible drive. So you are left with the question: Should I stick with my NAS vendor's list of approved drives?
I queried three vendors who put their products' reputations on the line by producing only BYOD NASes: Synology; Thecus and QNAP. I also contacted NETGEAR, whose ReadyNAS line depends on a mix of factory and user installed drives.
I asked them all three questions:
- Why do vendors need to qualify drives for NASes?
- What does their drive qualification consist of?
- What risk do users take from not using vendor qualified drives?
The main reasons given for the need to qualify drives were compatibility, reducing troubleshooting and support variables, reliability and eliminating known problem drives. Of these, compatibility and reliability are probably the chief concerns. The next section describing the qualification procedures will clarify these further.
NETGEAR and QNAP also pointed out the need to ensure a match between a drive's intended application and its use. NETGEAR noted that its ReadyNAS home (Duo, NV+ and Pro Pioneer Edition) and business versions carry three and five year warranties respectively. So they choose their factory-installed drives accordingly. This can result in noisier business systems that run hotter, but that's the price paid for performance.
A visit to the ReadyNAS Hard Disk Compatibility List page, however, doesn't break out the drives according to product line. NETGEAR said the list is applicable to both product lines, but typically is used by people buying the empty chassis "home" products. They plan to establish separate home and business approved drive lists as they broaden their "business" product line and qualify new drives and drive vendors also continue to separate their product lines.
QNAP said they take drive vendor application recommendations into account for their approved drive lists. They didn't get into specifics, citing confidentiality issues. But they said that drive vendors' application recommendations do affect QNAP's drive choices.
Thecus cited four main reasons for qualification: drive firmware bugs; power consumption; thermal issues and SATA spec compliance. They mentioned two notable cases of problems with Western Digital and Seagate drives that had to be addressed via drive firmware upgrades. For power, startup power is a bigger concern than steady-state draw, since the power spike produced during drive spin-up can cause drives to not come up in time to be mounted and result in RAID failure.
The SATA spec compliance issue touches on issues caused by host-controller work-arounds for non-compliant drives. According to Thecus, while all SATA drives claim SATA I or II compatibility, "almost all" SATA host controller device drivers implement workarounds for some drives and don't work at all with other "black list" drives.
If one of the black list drives is used, it may fail to work or be detected by some SATA host controllers. And even if a drive is in a controller's " workaround table", it may not be able to operate at full speed with that controller. So to avoid possible data loss or performance degradation, these drives aren't included in approved drive lists.