Data: DEGRADED on RN104

As far as the lost connections go, it is best to follow whatever advice mdgm gives you after he analyzes your logs.

njpryan wrote:
I have noticed of late that the space available has suddenly increased from 2GB (approx) to 4GB (approx) for no apparent reason.

Do you really mean GB? or TB?

Do you have snapshots enabled?

njpryan wrote:
With regards to the earlier conversation about RAID-1 and RAID-5 when I add the third 4TB drive - what is going to happen - e.g. will I have 12TB of storage or 8TB of storage and 4TB(slot 2) remains backup of Slot 1 - sorry in advance for seeming confused and repeating some questions.

With xraid2, 2x4TB uses standard RAID 1, and gives you a 4 TB volume. When you add a third 4 TB drive it is automatically converted to RAID-5, and you end up with an 8 TB volume with single redundancy. Slot 2 will no longer be a mirror for slot 1 (as I said above, raid-5 redundancy is more complicated than that). Instead 4 TB's worth of redundant parity blocks are distributed across all 3 drives. This allows any failed (replaced) drive to be reconstructed from the other two.

The basic idea is that if Sector X on drive 1 and drive 2 are allocated for data, then Sector X on drive 3 is allocated for parity (and is the xor of the sectors X on drives 1 and 2). xor is a mathematical operation ("exclusive or") that operates independently for each bit in the sector.

0 xor 0 = 0
0 xor 1 = 1
1 xor 0 = 1
1 xor 1 = 0

It turns out that if

a xor b = c
then
a xor c = b
and
c xor b = a

So you can reconstruct any one of the sector X's from the other two. The parity block pattern is rotated (so 1/3 of the parity blocks are on each drive).

This recovery operation scales to 4 or more drives. Because if
a xor b xor c = d
then
a xor b xor d = c
and
a xor d xor c = b
and
d xor b xor c = a.

So again, any single block that is missing in the "stripe" and be reconstructed from the remaining blocks.

If two or more blocks are missing in the pattern, then RAID-5 can't fix it.

Also, note that when you replace a disk, RAID-5 knows for certain which blocks need to be reconstructed. But if one of the blocks is somehow silently damaged (but can be read) then a xor b no longer equals c. RAID-5 can't figure which one is corrupt w/o help. The bit-rot protection feature in OS6 can (sometimes) figure out which block is bad, and reconstruct it according to the above formulas.

This is also why disk cloning is a last resort when repairing raid - it conceals which blocks are damaged, so there is almost always some file system corruption that RAID cannot repair.

Hi StephenB,

Been a while since I was able to reply - apologies for that - I think I am unable to grasp the while RAID thing still.

With regards to the first replay - yes it is GB and not TB the change size is.
I do have snapshots enabled but not for all folders

Now to the more complicated (for me :) ) my NAS setup
Currently with 2 of the 4 bays filled with both 4TB HDD's and currently set at RAID -1 which as I understand it as Slot 2 being a complete backup of Slot 1 - so while having 8TB of storage I actually have 4TB of storage and 4TB as backup.

Now here is my next step. I now have just received my 3rd 4TB HDD for Slot 3 (not installed yet as waiting gone your superb advice to date !!)
While I currently cannot connect to my NAS using the web due to it continuously being offline and presuming this is something to do with it being busy with all my data as only 9% of free space left I have a question (eventually !) can I turn off the RAID on the NAS now prior to inserting the 3rd HDD and what effect will it have on the SLOT 1 and 2.
Also if I just insert Slot 3 now I know you told me that it would change the RAID from 1 to 5 - what exactly would I have storage wise to work with ? Slot 1 4TB Slot 2 ? Slot 3? considering that the toal would be 12TB.

I obviously won't turn off the RAID if this would cause issues with my data etc and I won't do anything until I hear back from you.

Many thanks :?

I don't think I'd insert a new drive if the web interface wasn't responding. That's a sign of trouble. Maybe mdgm can comment...

On your other questions:

-You can't turn off raid unless you delete your existing data volume and switch to flex raid. That will destroy your existing data. If you decide to do it, create one volume for each disk.

-If you hot-insert drive 3 with the default xraid2, when the rebuild completes you will have 8 TB (~7.2 TiB) of storage, and protection any any single disk failure. Adding a fourth drive would bring you up to 12 TB (10.9 TiB).

If you want to protect your data properly you need an independent backup on a different device (even with RAID-1, and certainly with RAID-5). Try not to think about RAID as being a "backup"- it really isn't. By analogy, RAID is like having a spare tire in your automobile. If one tire goes flat, you are still good to go. But it doesn't protect from multiple flats, and it doesn't protect from engine trouble, battery failure, ...

Hi StephenB,
Thanks for the replies.

Worried about your comment on the sign of trouble.

My NAS is on 192.168.1.1
But when I type in the address is used to be fine but now it appears with the following:

/Users/niallryan/Desktop/Screen Shot 2015-06-30 at 21.25.06.png

This has been appear for a while now - I have clicked on the Re-Connect several times and the screen re-appears. the only way to resolve it is to power off the NAS and re-start it and then it works fine for a while before re-appearing. The length of time working before the message re-appears is not consistent.

When you say that you wouldn't insert the third drive - why ?

I know magma did ask me to send logs but guess what ?? How ?? :)

Thanks

I can't see your screen shot. It needs to be in some cloud server like Google Docs or photobucket - you appear to have tried to share it directly from your desktop.

The web ui should respond - the fact that it isn't suggests that your system might be under very heavy load. It'd be best to understand why before proceeding.

On logs, you can try RAIDar 6.0 - if it sees the NAS it should give you a "download logs" control.

Ah, sorry about that forgot what I was doing there. It was just a screenshot of the offline screen.

I downloaded and installed RAIDar 6.0 as suggested and yes I can download whatever logs are required, I had an older version, thanks !!

Web IU - This was my conclusion also that as there is only 9% of disk space left, I do remember seeing the following in the logs on the UI as follows :
Volume: Volume 'data' usage exceeds 90 % of size (3.6 TB).

I eventually decided to do what is the only option and that was to unplug the NAS and restart it again and this works then for a time. RAIDar 6.0 has a re-start button but could not do it as it could not connect to the NAS as it could not be found.

Anyway the NAS is back up and running now and everything is appearing normal for now. For how long, I don;t know. But if mdgm does come on board here and let me know what logs he requires then I can send then to him.

I suppose I will have to wait and hold off on installing the 3rd HDD for now but time is running out for me as the Data is important. I am wondering if the above conclusion is correct surely adding the 3rd HDD will remove the issue of the device being under a heavy load as you put it with the extra storage.

Talk later

NJP

Perhaps manually delete snapshots, and if you can get the free space up first.

Send in your logs (see the Sending Logs link in my sig).

Hi mdgm,

Thanks for coming back - have sent logs there earlier

Looking forward to your response

Regards

NJP

Sent you a PM