A moment of enlightenment on disks.
I have a Synology NAS with 4 disks in it. Which disks should I be using?
Other manufacturers of disks are out there but I choose WD. Their range (2016) is...
- Blue - for the desktop primary disk
- Green - environmentally friendly, good for the desktop secondary disk
- Black - high performance, good for gamers
- Red - NAS specific
- Purple - for systems that write a lot and read little (eg. surveillance)
What makes a disk NAS specific?
Here's some raw information...
- For a standalone disk, returning data correctly is important - if a sector is bad, disks will often try many things to get the data (and then mark that sector as bad).
- In a RAID, it's the RAID controller's responsibility to return the data correctly.
- Most NAS are configured as RAID - if one of the disks has a bad sector, it's no biggie. One of the other disks will have the data.**
So, if we use a desktop disk in a RAID and a bad sector is read, the disk can spend a long time (tens of seconds) trying to get the data. Totally unnecessary and the RAID controller might think that the disk has died!
Luckily, the Red disks are configured with Time Limited Error Recovery (TLER) which means the disks can quickly tell the RAID controller it can't get the data, mark that sector as bad and move on.
There's more complication if the RAID controller sees a bad disk and tries to do a rebuild by checking all disks for errors but discussion of that is for another day.
Western Digital's NAS specific Red disks might be a few pounds more expensive than others but they allow the NAS to do a better job of returning the data speedily. Additionally, you don't run the risk of needing to replace a whole disk just because one sector went bad.
* Originally the "I" stood for Inexpensive
** Not completely true but let's suppose the RAID is configured to survive failure of one of the disks. Mine is. 8-)
Here's a youtube video to get you started.