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Author Topic: Breaking and resynching RAID-1  (Read 6345 times)

DimiPana

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Breaking and resynching RAID-1
« on: March 22, 2011, 07:07:55 PM »

Hello!

I just purchased two Seagate Barracuda ST32000542AS (2T) and would like to know what is the recommended procedure to install them.

My DNS-323 is currently configured with two Seagate Barracuda ST31500341AS (1.5T) in RAID-1. The existing volume is about 25% full.

Should I remove the one drive and install the new 2T one and expect that the DNS-323 is smart enough to rebuild the broken RAID-1, then remove the remaining 1.5T drive and install the second new 2T one and -again- have the nas box re-sync the RAID-1? Will that work?

-OR-

Should I proceed another way by moving all data to a safe place then install the two 2T new drives, format them, create the RAID-1 and move the data back to the nas box?

I guess, from a time perspective, option #1 will take less time but I just don't know if the 323 is able to do a full resync with a new drive. On the other hand, option #2 is definitely tried and tested but it will probably take way much longer.

Can you please point me to the correct direction? Obviously, the value of this data is priceless.

Thank you very much!
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JimD

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Re: Breaking and resynching RAID-1
« Reply #1 on: March 23, 2011, 02:41:24 AM »

Option 2 is what you want. The 323 will format the 2T drive to match the existing 1.5T. You'll end up with a 1.5T raid, and a 500 gig 2nd volume.

Copying off, and installing both 2T drives will give you the larger raid.

Jim
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fordem

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Re: Breaking and resynching RAID-1
« Reply #2 on: March 23, 2011, 06:38:30 AM »

Thank you very much Jim, for the prompt and clear response. I better start copying then. I am lucky that the data is only around 300Gb this is doable even with an external USB. But the more I think of this, what will happen in a scenario where -say- one has a full 1.5T of data and wants to increase the RAID-1 to 2T or more. In other words you always need an equal amount of storage elsewhere every time you want to transfer data and install higher capacity HDs. I am surprised there is not a way for this DNS-323 to do it with a procedure like my option #1.

Thank you again very much!

Based on these comments, it would appear that you a) don't already have a backup and b) lack the capacity to make a full back up.

Contrast that with ...

Obviously, the value of this data is priceless.

If you value the data, then you need to back it up - RAID is not a backup.  If the data is priceless, then investing in the necessary storage capacity to make a backup, should not be an issue, imagine the cost of losing it if the NAS failed, or the data becoming corrupted.
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RAID1 is for disk redundancy - NOT data backup - don't confuse the two.

fordem

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Re: Breaking and resynching RAID-1
« Reply #3 on: March 23, 2011, 12:29:01 PM »

Fordem -

Your post does not answer my question but -partially- I see your point.

Where in my previous post did I say that I do not have a backup?

You did not - you inidcated you were about to start copying the data to a different location - if you already had a current backup, this step would not have been necessary.

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I disagree with the blanket statement that RAID-1 is not a backup. A more appropriate thesis would be that "RAID-1 is and is not a backup depending on how you use it". If RAID-1 is the volume where your OS (and data) resides, YES you are right it is not a backup. But if a RAID-1 volume is where you store a copy of your OS/Data then it is by definition a backup (with the "safety-net" of redundancy).

Disagree all you want - if you have your workstation backed up to a NAS containing a RAID1 array, then the NAS is the backup, it would still be a backup if it contained a single disk.
--

Quote
So back to our subject, I have a RAID-0 workstation (I do a lot of video editing) that backs up daily (OS and DATA as images and files) into the DNS-323 which is configured as RAID-1.

If you are asking me if I have a backup the answer is YES because if one HD in the NAS fails I still have the other HD to rebuild from it.

As I mentioned before - the backup is the NAS whether it is RAID1 or a single disk.

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the answer is NO if you're asking me whether I have a separate (2nd) NAS to backup my (1st)
backup.

Now you're getting the idea - the NAS is the backup not the RAID.

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The issue at hand depends how big is currently the NAS Volume. If the DNS-323 will not allow to insert a higher capacity HD (2T > 1.5T) format the full 2T and then sync the 1.5T remaining HD with the 2T HD then there is a serious space problem. Data from the existing 1.5T RAID-1 has to be transfered somewhere while the 2T RAID-1 can be crated.

Not if you already have a copy of it elsewhere.

Quote
But how about this:

Properly shut down the NAS and insert both the 2T HDs and create the RAID-1.

Then, either

1) Remove one 2T HD (i.e. break the RAID-1) and insert the "old" 1.5T HD. Will the NAS sync the 2T from the 1T or will it get confused. If a snafu happens, I still have the other 1.5T HD with the data intact, right?

2) Or, (and I like this better) leave the newly created 2T RAID-1 as is, connect either one 1.5T HD (or maybe both?) in another PC and boot from a Linux (Ubuntu) disk, hoping that it will recognize the data on the 1.5T HDs, therefore allowing me to copy from this PC to the NAS.

Call me lazy, but there should be a way to do this without having to move the data twice, it's just time consuming.

Thank you all for your feedback!

How about this - remove both 1.5T disks from the NAS, label them and set them aside - install & format the new 2TB disks into a RAID1 array, and then copy the data off your workstation to the NAS - how's that for simple?

Should a mishap occur, you can simply shutdown the NAS and reinstall the 1.5TB drives being careful to place them in the bays from which they were removed, and then power it up - your data should be intact.

Bottom line is this - and it's your decision - the data is priceless - are you willing to trust a stranger on the internet to tell you how to deal with it, or are you going to create another backup because if sh!t happens and that stranger is wrong, you've lost it all.

Tell me now that your RAID1 is backup sufficient to protect you.
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RAID1 is for disk redundancy - NOT data backup - don't confuse the two.

GregQ

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Re: Breaking and resynching RAID-1
« Reply #4 on: March 23, 2011, 04:10:02 PM »

Hi DimiPana,

To answer you original question. You would want to go with option 2. First backup your data from the 1.5TB drives (to another location), put in your new drives, reformat and then copy your data back over.

As JimD mentioned, doing it this way, you will utilize the full disk capacity for your RAID.
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