Is it sane to build a machine with RAID 5 expecting to hold around 5 Tb (and able to grow) with 1.5 or 2 Tb SATA II disks?
It will be used as audio and documents storage. I already have chosen a chassis with 16 3.5" hard drive bays. Now I'm thinking about what to put on those bays.
Pros I see:
- Cheaper per Tb
- Greater extensibility per chassis (3 times max capacity using 1.5 vs. 0.5)
It's the cons I'm wondering about. I expect using big disks to be slower, but is this really the case? I don't know about failure rates between small and big drives, are big ones expected to fail more often?
So, two questions:
What are the cons of building a 5Tb RAID5 with big disks?
Any particular drive model you'd recommend for either big (2Tb) or small (0.5Tb)?
Using RAID5 with this configuration, you introduce additional risk to your RAID. With the storage density introduced with modern disks, the likelihood of encountering a bad block on multiple disks is higher.
If using 1TB+ disks, it's recommended to use a RAID6 as opposed to RAID5, as it has an additional parity disk.
If you want greater speed as well as better guaranteed availability, you might consider RAID 1+0 as well.
As far as speed, compare the seek time and various other specifications. Speed does not vary much with commodity disks that are higher density. When I bought disks a few months ago, the largest tier1 SAS disk I could buy was 450GB.
You had me a R5 - don't.
The reason is that in the event of a disk failure you have zero protection until you've replaced the disk and the array has rebuilt.
For large cheapo SATA disks this rebuilt process can take DAYS - meanwhile you are at the mercy of a second disk failing - at which point it's game over.
Also this type of disk is rarely happy to work solidly 24 hours a day and I've seen rebuilds kill disks - again making the whole thing rather dubious.
If you can use RAID 10 over 5 or 6, if you insist on 5/6 then use 'enterprise' disks capable of a 24/365 duty cycle.