How important/useful is dual-bay (RAID1 mirror) in a home NAS, with cloud backup?

[d000hg]

I'm finally set (I think) on Synology for the long-anticipated NAS we want primarily to centralise MP3s (for chrome-cast around the house) but will also use as a generic central dump for photos, videos and any files we want to keep accessible and/or backed up.

I'm pretty sure we might splash out on several Tb of cloud storage and just sync the whole damn thing and be done with it, rather than spend days figuring out which files we want backed up and which we can handle losing. Not sure if my work stuff will go on this too but we 100% WON'T be relying on the NAS for day-to-day critical files so if it died it would be inconvenient having to rebuild it, rather than urgent.

As such, I am trying to decide if the extra convenience (not security, RAID isn't backup!) of dual-drives is worth it for the chance a drive fails. As I see it, ALL this saves me is the time repopulating a new drive from cloud (maybe we keep physical backups of really weighty files on a USB drive just to save download).
Roughly speaking it seems the low-tier 2-bay enclosure is about the same price as a medium-tier 1-bay (Synology DS218J Vs DS118) and of course the drives will cost 2X as much - so I can get a considerably more powerful 1-bay setup quite a bit cheaper than an economy 2-bay.

I have never ever had a hard disk failure so it seems to me a tiny risk... trying to work out the risk/reward of spending more on the insurance of RAID. It's not like I use it in any of my PCs.

Thoughts and expert advice welcome.

[northernladuk]

I have never ever had a hard disk failure so it seems to me a tiny risk... trying to work out the risk/reward of spending more on the insurance of RAID. It's not like I use it in any of my PCs.
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Tiny risk. Massive headache. You've been lucky. Can that luck go on for ever?

If you ever did experience a harddrive fail you wouldn't be asking this question.

You've been lucky so far. Be happy with that and spend a few 10s of pounds more to make sure you don't have to rely on luck.

It's amazing how critical the files you do lose suddenly become when they are gone forever.

[NotAllThere]

I have a Synology. 4x4TB, using their SHR-2 (effectively RAID 5). I have windows file history from 1 laptop and 2 desktops running onto the NAS. I've also got 1 desktop and 1 laptop using Cobian Backup onto the NAS.

The point is you don't need a backup until you need it . And you don't need RAID 5.... until a disk fails, and your redundancy is gone. I've been running it for over a year now, and one drive is reporting SMART errors. I'll address that when I get back from holiday.

It's important to make sure that your individual HDD are from different batches, even different manufacturers. 4TB is the maximum size you should use.

[BackupBoy]

Yes it is and get a BackBlaze account for the Synology too.

[malvolio]

Important to remember that RAID5 is not a backup solution, it's a risk mitigation one and if you lose a disk, you lose RAID5. If you swap a disk out there will be a fair period while the RAID5 set is rebuilt. Calculating reliability from the MTBF shows that reliability is actually no different to a single disk configuration.

I run mine in a RAID 0,1 format, so if I lose a disk I'm also back to what is effectively a single disk but recovery is a lot easier - just put in a replacement disk. There's also a performance gain since you can read from either disk although writing slows down by about 5%. Reliability goes up by a factor of at least 100%.

Sensible datacentres (they do exist) use both, shadowing virtual RAID5 set across separate drives but that's probably overkill for our kind of usage.

Whatever you do, you need a backup regime in place as well. I use the NAS's incremental backup regime to an attached 1Tb USB drive which I tidy up every so often.

[NotAllThere]

Important to remember that RAID5 is not a backup solution, it's a risk mitigation one and if you lose a disk, you lose RAID5. If you swap a disk out there will be a fair period while the RAID5 set is rebuilt. Calculating reliability from the MTBF shows that reliability is actually no different to a single disk configuration.

Source please.

You seem to be saying that the whole idea of RAID 5 is wrong.

[malvolio]

Source please.

Source is 30 years of technical and service architecture work...

You seem to be saying that the whole idea of RAID 5 is wrong.

No, I'm saying RAID5 is a BCP option, allowing you to continue working following a physical failure at a reduced capacity. It is not a DR-preventing one. RAID5 volumes in a RAID0,1 configuration is the only disaster tolerant solution.

[vwdan]

Source please.

You seem to be saying that the whole idea of RAID 5 is wrong.

RAID 5 is VERY out of vogue nowadays - it's not particularly well regarded any more when better options such as 1+0 and 6 exist. A lot of people have found to their detrement that the R5 rebuild process is pretty harsh on the other disks and if a second fails before the rebuild you're up the creek.

Saw it loads back in my 2nd line days at an MSP - standard server load out was R5, so we'd toddle out, replace a disk and set off the rebuild which could take hours and hours. It wasn't unusual to then receive the "servers gone" call the next day

[d000hg]

Tiny risk. Massive headache. You've been lucky. Can that luck go on for ever?

If you ever did experience a harddrive fail you wouldn't be asking this question.

You've been lucky so far. Be happy with that and spend a few 10s of pounds more to make sure you don't have to rely on luck.

It's amazing how critical the files you do lose suddenly become when they are gone forever.

I think you've missed the point. It would be backed up - all my important files already are (accounts, code, etc). You'd be a fool to trust RAID as your backup solution in case your house catches fire or a power surge takes it out.

The question is specifically about removing the headache of having to USE the backup. As I see it, with RAID you are almost certainly never going to need your backup barring fire/theft/lightning but without it, there's an appreciable chance you will.

If it is storing files I don't need day-in-day-out then is having to re-sync a new drive from my cloud backup (that could take a few days) a problem basically? Is RAID worthwhile to protect my MP3 collection?

[d000hg]

Yes it is and get a BackBlaze account for the Synology too.

How is Backblaze preferable to anything else one might use (OneDrive, Google, DropBox, etc)? It looks great from their blurb but what is the USP or advantage?

One issue I have is speed of these cloud providers... I rarely get download/upload speeds close to what my ISP supports which suggests a bottleneck somewhere. If you have to rebuild from backup you want to get 20Mbps not 2