Hi,I have just recieved my ReadyNAS Ultra 4 with 2 2TB drives. They are seagates so just to be safe, I am testing them with seatools, which will take many hours.While that is happening I thought I would read up on the different types of raid. Xraid2 sounds impressive and mentions that it will mirror the contents of my data but this is what I do not understand. I have read the documentation and this explanation .. http://www.readynas.com/?cat=54 . What confuses me is this though. I do understand that if I have 2 drives, the contents of drive 1 will be duplicated to the contents of drive 2, much like raid1.What I do not understand though is that the guide says that if you add a further 2 disks to your NAS so that you have 4 in total, then you will have the capacity of the 1st 3 discs and the 4th disc will act as the mirror. How can this be though, if I fill up the contents of the 1st 3 discs how can the 4th disc mirror all of that data if I was to fill them 100%? Surely I would need 6 discs?? 3 drives mirrored onto another 3 drives???I just need to understand and know 100% that my data will be safe, otherwise I will have to use good old raid1.

Actually, X-RAID (and X-RAID2) is pretty much an expandable RAID 5, rather than RAID 1. The Duo/Ultra2/Pro2 are limited to "mirroring" due to the fact that they only have 2 drives.http://en.wikipedia.org/wiki/RAID_5#RAID_5FWIW, I have 2 ReadyNAS devices at home, 1 at my dad's and 3 at work and I only use X-RAID. There's no proprietary file system, either. Drives from a ReadyNAS can be mounted in a standard linux box in the event that the ReadyNAS hardware fails. For example, here are the instructions for mounting drives from a Sparc-based CPU - http://home.bott.ca/webserver/?p=306.

Thanks for the info, I also checked out this very clear and concise video which helped clear things up in my head http://www.youtube.com/watch?v=LTq4pGZt ... re=related .So just to be really clear, if I have 3 or 4 drives in my ultra4, I can only loose 1 drive and still have my data available? If I loose for example 2 drives out of 4, then I loose everything?Thanks for the linux link, would that info also work for drives in an x-raid2 config from a x86 based Readynas?

Yes X-RAID2 on the Ultra 4 protects against a single disk failure.On the Ultra 6, there is optional dual-redundancy to protect against two disk failures.It's actually simpler to recover data from a x-raid2 volume. x86 ReadyNAS use the standard 4k block size. Should be similar to mounting a software RAID volume taken from one linux PC on another PC.

Thanks for the quick reply. What I shall do then is buy a spare 2TB drive for an emergency swap just in case, best to be safe. If I had more £££ I would setup a system which would back up this NAS to another NAS off site, maybe one day :).Just on the mention of 4k block size. Is there a simple of way of figuring out if the drives in my readynas ultra4 are formatted with 4k rather than 512byte?

Don't confuse the block size of your volume with 4k sector partition alignment.Your partitions would be aligned for 4k sectors if your NAS came with 4.2.12 or later, which I think it should have. You can confirm that the NAS came with 4.2.12 or later by looking for the oldest version of RAIDiator in initrd.log. This file is included in the zip file downloaded when you go to Status > Logs > Download all Logs.

Fully understanding Xraid2 | NETGEAR Communities

11 Replies

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dbott67
Guide
May 20, 2011
Actually, X-RAID (and X-RAID2) is pretty much an expandable RAID 5, rather than RAID 1. The Duo/Ultra2/Pro2 are limited to "mirroring" due to the fact that they only have 2 drives.

http://en.wikipedia.org/wiki/RAID_5#RAID_5

FWIW, I have 2 ReadyNAS devices at home, 1 at my dad's and 3 at work and I only use X-RAID. There's no proprietary file system, either. Drives from a ReadyNAS can be mounted in a standard linux box in the event that the ReadyNAS hardware fails. For example, here are the instructions for mounting drives from a Sparc-based CPU - http://home.bott.ca/webserver/?p=306.
dented
Aspirant
May 21, 2011
Thanks for the info, I also checked out this very clear and concise video which helped clear things up in my head http://www.youtube.com/watch?v=LTq4pGZt ... re=related .

So just to be really clear, if I have 3 or 4 drives in my ultra4, I can only loose 1 drive and still have my data available? If I loose for example 2 drives out of 4, then I loose everything?

Thanks for the linux link, would that info also work for drives in an x-raid2 config from a x86 based Readynas?
mdgm-ntgr
NETGEAR Employee Retired
May 21, 2011
Yes X-RAID2 on the Ultra 4 protects against a single disk failure.

On the Ultra 6, there is optional dual-redundancy to protect against two disk failures.

It's actually simpler to recover data from a x-raid2 volume. x86 ReadyNAS use the standard 4k block size. Should be similar to mounting a software RAID volume taken from one linux PC on another PC.
dented
Aspirant
May 21, 2011
Thanks for the quick reply. What I shall do then is buy a spare 2TB drive for an emergency swap just in case, best to be safe. If I had more £££ I would setup a system which would back up this NAS to another NAS off site, maybe one day :).

Just on the mention of 4k block size. Is there a simple of way of figuring out if the drives in my readynas ultra4 are formatted with 4k rather than 512byte?
mdgm-ntgr
NETGEAR Employee Retired
May 21, 2011
Don't confuse the block size of your volume with 4k sector partition alignment.

Your partitions would be aligned for 4k sectors if your NAS came with 4.2.12 or later, which I think it should have. You can confirm that the NAS came with 4.2.12 or later by looking for the oldest version of RAIDiator in initrd.log. This file is included in the zip file downloaded when you go to Status > Logs > Download all Logs.
dented
Aspirant
May 21, 2011
Thanks for the info, the unit claims to have had 4.2.13, which I have since updated to 4.2.17. I have 2 Seagate Barracuda Green 2TB ST2000DL003 drives which do have the 4k aligned sectors.
xtrips1
Aspirant
Sep 29, 2011
If someone here fully understand Xraid2 then here is some challenge.
I have been stuck for the last 2 days trying to undelete around 7 TB of data from 6 X 3TB HDDs from my ReadyNas Pro.
For that I opted to use R-Studio.
But I need the following info to make it work and Netgear, well, I am still waiting for them to give me those answers.
So here are the missing parameters:

- Offset for every drive (usually the same for all drives, but can be different)
- RAID type (RAID0,1,5,etc)
- Block size
- Block Order (Left Synchronous, Left Asynchronous, Right Synchronous, Right Asynchronous or Custom)
- RAID algorithm / RAID layout (this is basically the way RAID adapter or controller writes data and parity blocks onto physical drives. They're standard ) in case of non-standard RAID layout you need to manually configure Data Blocks and Parity blocks distribution and numbers of rows.

Any help is welcome.
I am desperate.

Thank you
lool
Aspirant
Mar 30, 2012
Guys,
Perhaps it's obvious to you...but I'm a bit confused.
I do have two drives - 1TB with sector of 512 bytes and new 2TB drive with 4K sector size.
Would it be possible to run X-RAID2?
Will it work smoothly or are there any side effects? Maybe it's better to buy another 4K drive (but I'd like to spare some money at this time).
StephenB
Guru - Experienced User
Mar 31, 2012
It will work, but you will only get 1 TB of storage (with redundancy). I suspect that is not what you want.
DempaX
Aspirant
Jul 12, 2012
How much space would be avail using 2x1.5TB + 2x2TB in an Ultra 4? 2TB reserved for redundancy and potentially "5TB" left for storage?