Drive order matters w. RAID 5?

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virtualritz

Drive order matters w. RAID 5?

Post by virtualritz » Mon Nov 16, 2015 6:31 am

I had to sent my QNAP 469L NAS in for repair and took the four drives out for that. But I forgot to number them!

Now I wonder if I'm screwed if I put them back in the wrong order. If that were the case, could I use R Studio to find out the original drive order?

I think I once heard that if the device has drive roaming ability, the mount order should't matter with RAID 5.
But I don't want to use trial and error to find out whether that is true and/or the 469L even supports drive roaming.

Cheers!

Alt
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Re: Drive order matters w. RAID 5?

Post by Alt » Mon Nov 16, 2015 9:20 am

Indeed, disk order does matter in RAIDs. Moreover, if you install the drives in a wrong order, the device may (may, not will!) treat them as new ones, and create a new RAID setup, deleting the info about the previous one.
You may use the RAID Autodetect feature in R-Stuido (available in its Demo mode), or use ReclaiMe Free RAID Recovery to determine the disk order.
Then connect the drives to the system and pray that its Slot 1 corresponds to Disk 1.
My expectation is the following: Slot 1 indeed corresponds to Disk 1 in the RAID, and QNAP 469L NAS will through a warning if it decides to create a new RAID. But these are my assumption rather than a conclusive statement.

Corsari
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Re: Drive order matters w. RAID 5?

Post by Corsari » Mon Nov 16, 2015 9:53 am

Hello
Drive orders in QNAP (generally) is respected

But BEWARE don't fit wrong drives in the wrong bays otherwise you'll seriously will fall in a complete RAID initialization

QNAP uses a filesystem that because of that initialization, will WIPE OFF and BLOW OUT all the directories levels, and their and files names.

So beware to check carefully serial numbers when you have finished determining the drives order. Also because on top I've written "generally", if you can, you'd better clone the single drives before to fit them back into bays.

Only during the current year, we have received already four QNAP cases where the customer just removing and or playing with drives, got the volume reformatted loosing all the directories tree and all the files names. If this happens, only a RAW recovery will be possible (files by types without original names and no directories subdivided)

Kind regards
Robert
Technical Manager @ Recupero Dati RAID FAsTec (Italy)

USEFUL RULES and GUIDELINES
1) What to check BEFORE begin a disk image/clone process [link]
2) Disks that are too slow while imaging/cloning them [link]
3) All my posts on this forum [link]

Data-Medics
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Re: Drive order matters w. RAID 5?

Post by Data-Medics » Mon Nov 16, 2015 11:08 am

Most hardware RAID 5 arrays (using actual RAID cards) write metadata to each drive which enables it to detect what order they go in and allows for migrating/rearranging drives without issue. However most home NAS boxes are generally just a Linux or FreeBSD software RAID. I'm not terribly familiar with QNAP's software (they don't seem very popular here in the northeast US) but if it is a Linux variant you can read the settings out using a a tool called mdadm on a Linux machine to see what it was, possibly even mount it to copy the files out.

If that doesn't work, then R-Studio is the next option. PM me if you need any help finding the settings. Should be able to help out remotely if necessary.

virtualritz

Re: Drive order matters w. RAID 5?

Post by virtualritz » Mon Nov 16, 2015 9:13 pm

When using mdadm (or R-Studio), do I need to have all four disks connected or can I dump the metadata one by one?
I just ordered a case from Amazon to do that but if I need all four connected simultaneously, I need to order three more.

Alt
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Re: Drive order matters w. RAID 5?

Post by Alt » Thu Nov 19, 2015 12:28 pm

If I'm not mistaken, those config files are in text, so you may read them one by one directly from the disks.
If you want to create a virtual RAID in R-Studio to copy the data, you need either connect all the drives, or image them and work with the images.

Data-Medics
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Re: Drive order matters w. RAID 5?

Post by Data-Medics » Thu Nov 19, 2015 1:56 pm

To just read the metadata using mdadm you can just do one at a time. To try and mount the array will require that all original members be present, and that's assuming that Qnap uses a normal Linux RAID. I'm honestly not quite sure if it does. If you are really stuck at some point PM me and I can try to walk you through some of it.

virtualritz
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Re: Drive order matters w. RAID 5?

Post by virtualritz » Fri Nov 20, 2015 2:44 pm

I read the metadata one by one, using mdadm --examine.

For each of them I got, at the end of the metadata dump, information like this:

Code: Select all

Device Role: Active Device <N> (0..3)
Array State: AAAA....................... ('A' == active, '.' == missing)
I presume the number, <N>, listed after 'Active Device' tells the slot the disk has to go into, in my NAS?

Alt
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Re: Drive order matters w. RAID 5?

Post by Alt » Mon Nov 23, 2015 12:02 pm

I guess yes, but I'm not a big expert in Linux RAIDs.

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