NAS trouble and RAID confusion.

[Lord of The Bins]

Hey guys,

 

Long time lurker - first time poster.

 

So I have a mystery of sorts, that I hope you can help me answer.

 

I work at a small production company, where we edit our videos of a NAS from Synology. Recently the NAS was unable to power on, which apparently is a common error with NAS enclosures from Synology.

 

We are a small operation, so we don't have a big IT-department to help us out, so it was up to me to figure out this mess. Long story short - Synology are sending over a new unit(but we are looking into other options long term, if these things simply stop working every 2 years).

 

It's supposed to be a simple operation to migrate the discs once the new unit arrives, but I thought it would good to know, what RAID configuration we were using.

 

The NAS was in place before I started at the company, so I ask the guy who helped us set it up, what the RAID configuration was? He insists that it's RAID 6 with one disc being a hot-swap backup.

 

Now I am confused. I now know we had 7 - 4TB drives in the NAS. We had just shy of 8TB of usable capacity. That can't be right?

 

As far as I can tell, we would get 8TB of useable capacity with 4 drives in RAID 6.

https://www.synology.com/en-global/support/RAID_calculator?hdds=4 TB|4 TB|4 TB|4 TB

 

The old IT-guy is sticking to his explanation, and I can’t get more information from him. The old NAS is no longer with us, so I can't check that.

 

So I was hoping that you guys could clarify whether, it’s possible to have a RAID 6 configuration with the setup, I have described.

 

If it’s not RAID 6, then what is it then?

 

But -  If we actually do have have RAID 6 configuration, wouldn’t there be better ways to do it? 8TB of drive space with 28TB worth of hard drives doesn’t sound right to me.  

 

I can add that we started out with only 4 drives, which gave us around 4 TB usable capacity, if that helps. Then there was added 3 more drives which doubled our usable capacity on the NAS.

 

[LukeSavenije]

are all the drives visible in windows? (assuming you're not using linux)

[NelizMastr]

Strictly speaking here, a RAID6 by default has two parity disks and a minimum of 2 data disks. The data disks are striped and the parity disks keep track of the data. In a 4 drive config with 4TB disks this would indeed equal to 8TB, of which you lose some to the binary translation and formatting overhead.

 

With 7 drives, you'd have 2 parity and 5 data, equalling 20TB of space. The only way you could have 8TB of space with this config is when using 2TB drives instead.

[Lord of The Bins]

2 hours ago, LukeSavenije said:

are all the drives visible in windows? (assuming you're not using linux)

As of now all the drives are in a box on my desk waiting for the new NAS. 

 

Synology has it's own OS, but I never got a chance to check if the drives was visible. It's one of those all-in-one devices - DS1815+

 The NAS was put together before I joined the company and it was dead, when I was tasked with taking a look at it. So I basically haven't had a change to look under the hood while the darn thing was working.  

 

This thread is partly about figuring out whether I being told some complete nonsense by an IT-consultant.

[LukeSavenije]

to keep it on what i know (i use windows for my nas). Raid 6 shouldn't use that much. It's safe to use for that, but it really shouldn't use 20 tb for rebuilding

[GlobalPentahedron Corp]

looks like you have found a flaw in the consultant's memory. Human memory is very error prone.

[scottyseng]

Yeah, I can't see how you'd end up with only 8TB of useable space.

 

7 drives, with one being a hot swap spare, so 6 drives (4TB x 6 = 24TB) in RAID6 should give around 15TBish of useable space. I have trouble seeing how it would be so little space free (Unless it was 2TB drives as mentioned above)

 

For example, I have 10 x 4TB (40TB) in my NAS in RAID6 and have 29.1 TB of space. The norm is RAID 6 gives you roughly 2/3 of the space.

[dalekphalm]

4 hours ago, LukeSavenije said:

to keep it on what i know (i use windows for my nas). Raid 6 shouldn't use that much. It's safe to use for that, but it really shouldn't use 20 tb for rebuilding

Have you visibly confirmed the drive size and count?
 

If so, then your IT friend was simply wrong, or something was misconfigured in the NAS.
 

Perhaps a large chunk of the NAS was set aside as an "internal backup", or was simply not provisioned and therefore is inaccessible to the network users.

 

Once the replacement NAS arrives, migrate the drives in and check what configuration they're using.

 

6x 4TB in a RIAD6 w/ a 7th hot spare is a good setup though.

[Helly]

On 9/19/2018 at 11:43 AM, Lord of The Bins said:

Now I am confused. I now know we had 7 - 4TB drives in the NAS. We had just shy of 8TB of usable capacity. That can't be right?

 

I can add that we started out with only 4 drives, which gave us around 4 TB usable capacity, if that helps. Then there was added 3 more drives which doubled our usable capacity on the NAS.

Something here doesn't add up. Were those initial 4 drives also configured the same? So hot spare and raid-6. Cuz then it would add up correctly but that is just a ridiculous way of setting up 3 drives. And if an earlier reply is correct not even possible... so how then were those initial drives configured? Cuz RAID-5 (which would make sense) would have given you 8TB of space, and RAID-10 (which would be the best setup for 4 drives) would give you the same. AFAIK there is no configuration that would make you end up with 4TB usable with 3/4 drives.

 

The only way i could explain the 7 drives with 8TB usable would be to add the new drives but not expand the array to use the space.

 

My guess would be that someone in that company got their numbers confused.