khizaraq wrote:
Can you tell me the Pros and Cons?
The bid pro for RAID is space efficiency. If you put four drives in a RAID 5 array, you only loose the capacity of one to have hardware redundancy. If you are mirroring or using file duplication like the original drive extender or products like drive bender offer you effectively loose half your useable storage.
The con to RAID 5 is complexity - especially with larger drives, rebuilding an array after replacing a failed drive can take a long time. If the drives were purchased at the same time, another one may fail before the rebuild finishes. That's why you see RAID 6 which is dedicating the space of two drives for parity error-correcting data and can withstand two simultaneous failures becoming popular. Recovery of RAID sets is also much harder if not impossible. So if two drives in a RAID 5 partially fail, you could lose all your data.
Calculating and writing the parity information out tends to slow writes with RAID 5 or 6. Calculating parity used to be a big deal and hardware RAID 5 was considered mandatory, but these days most computer CPUs sit idle. What we still can't get away from with RAID 5 or 6 is, every time you write data, the data gets written to its disk, then parity information is written to *every other disk*. Every disk is involved with every write, which is expensive from a time point of view.
Mirroring and duplication don't have those recovery issues, and since there is no parity information there is no write penalty. There is a slight benefit on reads since either disk may satisfy the read request - whichever one "gets there first" if you will.
With the capacities and prices per gigabyte being what they are, I tend to mirror more these days. If I'm on a server and I need absolute performance, I like what is often coined RAID 10. Multiple mirror sets (RAID 1) with a RAID 0 volume across the mirror sets. RAID 0 is just striping across multiple disks with no parity information. Provides a speed benefit, but no hardware fault tolerance. I use it on my workstation where I have multiple backups and the downtime of having to rebuild and restore the volume if I ever have a hardware failure isn't critical. That's usually not acceptable for a production server, so that's where building a RAID 0 array across multiple mirror sets solves the hardware fault tolerance issues.
But to me, that is overkill for a WHS
File duplication for critical or smaller files is finer, and backup copies of my larger media files like media for TV shows is more than sufficient for me. Being able to pop a flaky disk into my desktop computer and in a worst case scenario manually copy off whatever files I can more than makes up for the lack of space efficiency RAID 5/6 provides.
Then there are interesting technologies like FlexRAID that for large files that change infrequently offer "snapshot RAID" - disks in the pool remain formatted with their native file system (can be read in another computer) but drives can be added and dedicated for the fault tolerance parity information. Instead of being constantly updated in real time, the parity information is updated on a schedule.
It looks like the perfect solution for a volume dedicated to videos and movies. My only problem with FlexRAID is its not clear if it's free, beta, commercial or ??? Perhaps one day I will look at it more closely as I do think the snapshot feature of it is perfect for WHS