Replacing a drive in a NAS which is configured as RAID 5

[Spyone1]

Hi there all.

Hopefully this will be an easy one.

I currently have a Netgear ReadyNAS 104 in RAID 5 format, with drives as follows:

Drive 1 - 2Tb HDD
Drive 2 - 3Tb HDD
Drive 3 - 3Tb HDD
Drive 4 - 4Tb HDD

The total available space on this is currently 7.9Tb (I know why, this is not the problem).

I was thinking of replacing the 2Tb HDD with a 3Tb HDD, bringing the available space to 10.02Tb. I cannot afford more than 1 x 3Tb drive at the moment.

My questions are:
1. If I simply take out the 2Tb HDD and put in a 3Tb HDD, will the RAID 5 configuration repopulate the 3Tb HDD with all the information that was on the 2Tb HDD?
2. Otherwise, do I have to remove all the data from the entire array, reformat the array and then replace the data?
I can do option 2 if necessary, there is only 4Tb of data on there now, and I have 8Tb available outside the NAS without the new 3Tb drive.

I have done some research and have conflicting information. One set of sources says RAID 5 will automatically repopulate the data, the other set says the new drive will simply become unusable storage until I reconfigure the array.

Hoping someone can help clarify this.

[profJim]

Re: Replacing a drive in a NAS which is configured as RAID 5

I don't have first hand experience with raid setups, but the information at DO's and DON'Ts for RAID-5 Troubleshooting Without Data Backup, Setup and Maintenance looks pretty solid. It looks like doing an initial precautionary backup is a no-brainer and should always be done before you install a new disk in your raid 5 setup. Do you want to risk possibly loosing all your data in your array?

Note their one invariable law:

The One Law

Beyond the seemingly obvious facts, there is ONE fundamental law that should be tattooed on the brain of every computer system operator responsible for RAID-5 data storage:

* A RAID-5 rebuild procedure will ALWAYS FAIL unless ALL of the subsystem components, i.e. the controller and all hard disk drive members are present and accounted for, this means: verifiably working properly. Failed rebuild attempts are lamentable and make successful data recovery more difficult and potentially impossible.

[parsec]

Re: Replacing a drive in a NAS which is configured as RAID 5

"Hopefully an easy one" you (and me) wish...

What you can and cannot do with your RAID 5 array depends on the RAID hardware/software being used in your NAS box. I could give you some instructions for Intel's RAID, but that is not the same as what you are using.

No one can assume that every RAID implementation will work the same way, whatever "the same" is, if that is a standard, and whose standard is it? There are several, but that it just the data format, not what can be done managing drives in various RAID volumes.

What is being used for RAID in your NAS?

[profJim]

Re: Replacing a drive in a NAS which is configured as RAID 5

I assume that you are using the ReadyNas software/hardware raid.

Pages 32 - 38 in the ReadyNas software user manual are confusing at best, for me anyway.

It looks like pages 83 - 86 in the ReadyNas hardware manual describe replacing a single failed disk and this is similar to what you want to do.

Have you checked out the ReadyNas forum at: NETGEAR ReadyNAS • Index page ?

[parsec]

Re: Replacing a drive in a NAS which is configured as RAID 5

Prof Jim, I agree the software manual is a bit confusing, IMO due to the multiple configurations of RAID possible and the types of migrations available.

I agree that simply replacing one disk for the new one as described in the hardware manual is really the only option given Spyone1's intent.

From the software manual, Expand Storage Capacity section, there are two ways to accomplish that:

You can expand the storage capacity of an existing volume in two ways:

Horizontal expansion
Expand the volume by adding more disks to the volume.

Vertical expansion
Expand the volume by replacing disks in the volume with larger-capacity disks

Spyone1's intent is a Vertical expansion, by adding one larger disk. But then we see this in the manual about vertical expansion:

RAID 5 Replace 2 or more disks with larger-capacity disks

Two or more disks is said to be required. Which of course is where the confusion begins.

OTOH, IMO the manual assumes the use of ALL equal capacity disks from the start, and replacing them with larger disks ALL of the same size.

Spyone1's RAID 5 volume is limited in potential size by the 2TB drive, which limits the other drives to 2TB, correct? Changing the 2TB drive to a 3TB drive would then allow the wasted space on the other drives to be used. Is this what your goal is?

I can't tell you if that will work or not, given the manual. It might work, but I'm not sure.

Of course, we see this in the manual regarding adding drives:

To reduce the risk of data loss, NETGEAR recommends that you
back up your data before vertically expanding a volume.

As Prof Jim said, checking the ReadyNAS forum is your best chance for an answer.

[profJim]

Re: Replacing a drive in a NAS which is configured as RAID 5

.....and he can probably contact their tech support and/or create a new thread in their forum if he doesn't find an existing thread that makes it perfectly clear exactly what steps he should take.
Thanks for nuttin' for copying their text and my needing to read it again.....now my head hurts.....again.