Difference RAID 1 vs. RAID 5

[Bronko]

Hello!

Compared to RAID-1, RAID-5 has the advantage that more usable net storage space is created from the physical gross storage space of the disks.

Some time ago someone told me, however, that it is much easier to recover data from a defective RAID-1 due to the complete redundancy (i.e. in much the same way as from a hard disk without RAID) than from a RAID-5, where the data is distributed over three hard disks. I am thinking in particular of cases where the whole RAID system is broken. E.g. in case of a water damage it happens regularly that the RAID controller first writes randomly confused stuff on the disks, until it (finally) chews completely.

Is it true that it is easier to recover data from a DEFECT RAID-1 array than from a DEFECT RAID-5 array?

[Bernat]

This can easily be determined: RAID is not a backup. If the RAID system is so bad that it hits the wall, then hopefully you have a backup. The maximum amount you can lose depends on how often you back up your crate.

Back to the topic: RAID protects against one thing in particular: defects in RAID components. Especially against defective mass storage devices. If you look at the old comparison to the car, then the hard disks are something like brake pads or clutch discs. So wear parts. They break from time to time and have to be replaced.
The aim of the RAID is to keep the box running while it waits for the hardware to be replaced. For the defect of the RAID (i.e. the condition that the RAID itself is dismounted and not just a component) you have a backup.

So the question is which RAID will give you what you need in case of a LW defect. And the RAID-1 definitely has an advantage because it is a 1:1 mirror. So in case of an error you only have a reduction of the bandwidth for read accesses (because only half of the disks can be read - e.g. two instead of four).
The RAID-5 must replace the missing disk by calculating the missing data blocks from the parity blocks. This is associated with considerably lower performance in the event of a drive failure. I had once maintained a root server for a customer that was still running when a RAID-5 disk failed, but the performance was so poor that it was actually offline until both the disk had been replaced and the RAID had finished the resync. With a RAID-1, the server would probably have continued to function fully.

RAID-5 is then also much more resource-intensive when restoring the RAID with a new disk, since blocks do not simply have to be copied, but the parity blocks are recalculated.

RAID-1 and RAID-5 have a few other differences, but they have less to do with the error than with how many disks you write to at the same time (because Stripe-Set writes to distributed disks and Mirror has no advantage over a single disk in writing), but that has little to do with the failure mode behavior.

[geforceGTX]

Hello, sir,

I think Wikipedia explains the whole thing very well: https://fitmylink.de/tNkid

From a data security point of view, a RAID 1 or RAID 10 is the best. It delivers the best performance and is also the most fail-safe. In a RAID 10 system of 8 hard disks, we had in fact the case that 3 hard disks failed at the same time. Fortunately always in one of the RAID 1 arrays. We don't even use RAID 5 or RAID 6 for our backup systems anymore. The performance is simply too bad here.

You always have to find the middle way between performance, security and required storage space.

[Malte]

I can't sign this universally like this. I run a Raid-6 backup server with 10 hard disks and even if several vHosts overpump their LV backups with Gbit I don't have any performance problems. Of course you can find md1_raid6 at the top of the list. Much more resource-hungry are all the deduplication tools on the vHost side.
The performance, however, admittedly falls quite strongly when reading non-sequentially many small files, as is the case with hardlinked file-based backups, for example.

On a productive system which is not used as a pure and large data storage (NAS) I would recommend RAID1 or RAID10 in any case - easier to patch, more performant and less complicated and therefore inherently less error-prone.

[Bernat]

My initial question has not yet been answered. 

Is it as easy to recover data from a Raid-5 as from a RAID-1?

If yes, which data recovery software can AUTOMATICALLY restore the data from the RAID-5 parities (if not the (only) hard disk is broken) ?