Why the type of Hard Drive used in a NAS matters

, posted: 6-Apr-2013 16:10

I strongly recommend using WD Red or Seagate Constellation drives in NAS (Network Attached Storage) products. But why shouldn't you just use cheap Green drives, or regular Barracudas?

Drive Errors

When a normal desktop drive encounters a read/write error it will keep trying for a long time, and then take steps to rectify the issue (e.g. remap a bad sector). But there's a problem: during this process the RAID controller doesn't know what's going on, and will consider the drive unresponsive and drop it from the RAID array.

Rebooting the NAS or re-seating the drive will make the NAS realise everything is fine, it'll rebuild the RAID and you'll be back working. But in the meantime you've lost hours to the rebuild, and it'll happen all over again at the next read/write error.

Drives designed for RAID, such as the WD Red or Seagate Constellation, have a setting in the firmware to stop a read/write recovery operation after 10 seconds and just let the RAID controller do its job.

"Green" Drives

Drives designed to be "Green" or "Low Power" park the drive head after 8 seconds of inactivity. This is fine in a non-RAID scenario where the drive will be accessed briefly and then sit idle for a long time.

Where this really starts to hurt is in a RAID configuration. The problem is twofold:

Many of these Green drives have a slow spin-up speed. By the time the drive has spun back up, the RAID controller may have decided the drive is unresponsive and marked it as bad.

Each spin-up of the drive is very stressful on the drive and counts as a full "load cycle". A typical desktop drive is rated for 300,000 load cycles.
  • In a worst-case scenario where a file was being read/written to the drive every 9 seconds (meaning the drive will park between each read/write), that's 9600 load cycles per day. After 31 days the drive has exceeded its rated load cycles.
  • In a more realistic scenario, if a file is read or written (remember, this includes Autosave by applications and any type of database access) once per minute during an 8 hour work day, that's 2400 load cycles per week. After 125 weeks (2.4 years) the drive has exceeded its rated load cycles.
This technology is unfortunately becoming more common in desktop drives. While it was once restricted to just the WD Green, it's now also stealthily making an appearance in some Seagate Barracuda drives.

RAID is not a Backup

Always remember that RAID is not a substitute for backups.
  • If a second drive fails during RAID5 rebuild (more likely than you'd think, due to the stress rebuilding puts on the other drives) you will lose data.
  • RAID doesn't protect you from accidental deletion or overwriting, like a daily backup would.
  • Having all data in one place could mean trouble if your building suffers a fire or flood. Consider offsite backups or disaster-proof external hard drives.



Rather humerous sequence of events

, posted: 2-Jan-2013 00:59

The van in the driveway

I've been staying with a friend back in my hometown of Hamilton over the holidays, where we've been having a long-term LAN party. Over the last month or so, he's been woken up each day at 1am by someone driving into his driveway with their headlights on and then pulling back out. We happened to see it one night when we were in the driveway talking, but were too far away to see who they were or what they were doing.

Since we were awake and very drunk on New Years, we decided to camp out in the driveway and see who it was. There were about 6 of us all sitting in the driveway with our vodka, but the mystery van never turned up.

The bonfire

We decided to crank a little fire in the backyard tonight, after discovering a stash of wood offcuts under his deck. We also decided to get rid of the huge backlog of recycling, and burnt all of his paper rubbish. There were a bunch of Waikato Times papers there, still in their wrapping. Turns out that they burn really well. Thing is, this flat doesn't subscribe to the Waikato Times, they just keep turning up.

Mystery solved

We decided to camp out again this morning, just in case van guy turned up. We had a camera set up on tripod to capture the number plate (and scare whoever it was doing weird things in the driveway).

Sure enough, he turns up at 12:45am and pulls right up the driveway. We get a bunch of shots off on the camera and then ask the guy (who has his window open) what he's doing.

Turns out he's the Waikato Times guy. Who's been delivering it to the wrong house for a month. And the intended recipient never complained.

Simple answer which, in retrospect, we should've been able to figure out for ourselves!



I have a blog!

, posted: 13-Aug-2012 13:30

Figured it was time I started writing my opinions down for others to disagree with Tongue Out

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