WD Red 3.5″ 4TB and 2.5″ 1TB pack an improved NAS punch!
Last July, I went on a bit of a mini-rant about how using a bunch of drives not meant to be in a RAID could potentially lead to loss of the entire array from only a few bad sectors spread across several disks. Western Digital solved this problem by their introduction of the WD Red series. That series capped out at 3TB, and users were pushing for larger storage capacities for their NAS devices. In addition to the need for larger disks came the need for *smaller* disks as well, as there are some manufacturers that wish to create NAS / HTPC type devices that house multiple 2.5" HDD's. One such device is the Drobo Mini – a 4×2.5" device which has not really had a 'proper' NAS storage element available – until now:
Today Western Digital has announced a twofold expansion to their Red Series. First is a 4TB capacity in their 3.5" series, and second is a 2.5" iteration of the Red, available in both 750GB and 1TB capacities.
As a recap of what can potentially happen if you have a large RAID with 'normal' consumer grade HDD's (and by consumer grade I mean those without any form of Time Limited Error Recovery, or TLER for short):
- Array starts off operating as normal, but drive 3 has a bad sector that cropped up a few months back. This has gone unnoticed because the bad sector was part of a rarely accessed file.
- During operation, drive 1 encounters a new bad sector.
- Since drive 1 is a consumer drive it goes into a retry loop, repeatedly attempting to read and correct the bad sector.
- The RAID controller exceeds its timeout threshold waiting on drive 1 and marks it offline.
- Array is now in degraded status with drive 1 marked as failed.
- User replaces drive 1. RAID controller initiates rebuild using parity data from the other drives.
- During rebuild, RAID controller encounters the bad sector on drive 3.
- Since drive 3 is a consumer drive it goes into a retry loop, repeatedly attempting to read and correct the bad sector.
- The RAID controller exceeds its timeout threshold waiting on drive 3 and marks it offline.
- Rebuild fails.
- Blamo, your data is now (mostly) inaccessible.
I went into much further detail on this back in the intro to the WD 3TB Red piece, but the short of it is that you absolutely should use a HDD intended for RAID when building one, and Western Digital is removing that last excuse for not doing so by introducing a flagship 4TB capacity to the Red Series.