RAID, to?

Started Apr 22, 2013 | Discussions thread
Richard Veteran Member • Posts: 4,858
Sorry, you are incorrect in a number of ways.

Scott Eaton wrote:

>>>Raid 5 is more for uptime all the time.

RAID 5 uses a parity algorithm to allow three drives to store the same data as four drives.

This is absolutely wrong. If you have 3 1tb drives after Raid 5 you have the space of 2tb total. This is because 1TB of space spread across 3 drives is use for parity So you are incorrect. When a drive goes bad, you have 2 drives left with 2TB of information so your system will not go down. You ALWAYS lose 1 disk to parity. So your thinking is wrong, it does not give you more space, it give you less space

Wiki explains this

"RAID 5 (block-level striping with distributed parity) distributes parity along with the data and requires all drives but one to be present to operate; the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. RAID 5 requires at least three disks"

While in some instances you have hot swap / rebuild capability by far the majority of consumer based storage doesn't implement this.

Hot swap is another feature that has nothing to do with Raid5. Raid 5 allows your system to be up even though a drive fails. If you have hotswap, you don't have to bring your system down to replace the drive. If you don't have hot swap the computer still stay up until another drive fails, this is uptime all the time. The computer notifys you that the drive has failed. Then during a maintenance cycle, you bring the system down so you can replace the drive. You gain nothing and actually lose 1tb of drive space to have uptime all the time when a drive fails.

Hardware based RAID 5 is also notoriously fragile - far more than you are told. RAID 6 is a bit better in this respect, but a controller failure or error will wipe terrabytes of data in short order. RAID 6 just distributes the target better.

You are behind the times. Raid 5 when done correctly is quite reliable.

Software based RAID 5, aka many Linux NAS solutions are more hardened than hardware based because an over-heating chip won't write garbage to a sensitive parity stripe.

They are also much slower and I would say no more reliable. In fact if the OS has a problem, then the data does not get written to the disk.

Still, given the cheap cost of storage RAD 1 or 10 should be your first choice.

Raid1 and Raid 10 are not a substitute for a backup, but I would say Intel RST is the closest thing to a raid backup as you can get.

You need to go back and read documentation because raid5 does not do some file compression to give you more space, it gives you less and its primary function is for uptime all the time computing, nothing else.

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