With Dual Drive Bay Attached in Raid 1

[Lukasz Obara]

I have an ASUS RT-N66U running Tomato Shibby v.132. In addition I have entware-ng installed on a flash drive and a dual bay USB hard drive (Rosewill R2-JBOD) enclosure attached to the router that I use as a NAS. The enclosure has 2x 2.TB hard drives currently running as a JBOD so that I see one drive of 4TB. Since I don't have much data I plan on backing up what I have and reconfiguring the NAS so that I have a RAID 1 setup. I've checked the documentation for the Rosewill R2-JBOD and am sure that this is not feasible. I wanted to know if it was possible to use entware-ng to accomplish this.

I've looked into the rsync module, which seems like an interesting approach. But I'm unsure whether the NAS will appear as two separate drives or just one. Any help would be appreciated.

 

[ColinTaylor]

Looking at the Rosewill manual I'd agree with you that there's no indication that it's capable of doing RAID 1. In fact, it's "big" mode which you're using at the moment sounds like it might be non-standard. In which case when one disk fails you'll probably lose the data on both disks.

To do software RAID on the router you'd need kernel support for it (md) and mdadm which I don't believe the N66U has. At least not in Merlin, I don't know about Shibby (this is a Merlin forum after all).

So you're probably left with one option. As you said, reconfigure the Rosewill as a JBOD so the router will see it as two separate drives. Then use something like rsync to do periodic copies of one drive to the other.

 

[L&LD]

JBOD is not two separate drives. It is a form of RAID with no performance benefits (just capacity).

 

[ColinTaylor]

JBOD is not two separate drives. It is a form of RAID with no performance benefits (just capacity).

No it isn't. JBOD is Just a Bunch Of Disks. It is specifically not a RAID. https://en.wikipedia.org/wiki/Non-RAID_drive_architectures#JBOD

Granted, different manufacturers might have their own "interpretation" of the term. But in this case the device is either in JBOD mode where each drive is seen individually, or it's in "big" mode where the drives are concatenated into a single logical volume.

http://www.rosewill.com/media/Download_Files/user_manuals/usermanual-R2-JBOD.pdf

 

[L&LD]

No it isn't. JBOD is Just a Bunch Of Disks. It is specifically not a RAID. https://en.wikipedia.org/wiki/Non-RAID_drive_architectures#JBOD

Granted, different manufacturers might have their own "interpretation" of the term. But in this case the device is either in JBOD mode where each drive is seen individually, or it's in "big" mode where the drives are concatenated into a single logical volume.

http://www.rosewill.com/media/Download_Files/user_manuals/usermanual-R2-JBOD.pdf

Seems we may both be right, but Roswill makes me wrong.

 

[ColinTaylor]

With all due respect I think you were referring to a concatenation (aka span). A concatenation is not a JBOD. You can use a volume manager to make a concatenated volume out of the JBOD's disks, but the JBOD is still a JBOD.

 

[L&LD]

https://en.wikipedia.org/wiki/Non-RAID_drive_architectures

JBOD (derived from "just a bunch of disks"): an architecture involving multiple hard disk drives, while making them accessible either as independent hard disk drives, or as a combined (spanned) single logical volume with no actual RAID functionality.

Doesn't matter what we name we use to call a rose, it will smell as sweet.

 

[ColinTaylor]

Read further:

JBOD (abbreviated from "just a bunch of disks") is an architecture using multiple hard drives, but not in a RAID configuration, thus providing neither redundancy nor performance improvements. Hard drives may be handled independently as separate logical volumes, or they may be combined into a single logical volume using a volume manager like LVM; such volumes are usually called "spanned".[2]

When combined into a single logical volume, JBOD configurations are also called "linear", as separate hard drives are concatenated in a linear manner to form a logical volume. Due to its nature, no redundancy is provided with this configuration, meaning that failure of a single hard drive destroys the logical volume as a whole. mdadm, in addition to LVM, supports creation of such non-RAID linear volumes.[3][4]

The key phrase here is "using a volume manager". The JBOD presents each disk individually to the OS. It is the volume manager that uses these disks to create a new logical volume. A JBOD, by definition, only ever presents the individual disks.

 

[L&LD]

My point is that JBOD allows for definitions of 'spanned' disks.

What actually happens in the world is more pertinent than what the official definitions originally were.

 

[ColinTaylor]

Very true.

I suspect a bit of Microsoft-ism has distorted the original meaning.

 

[sfx2000]

JBOD is not two separate drives. It is a form of RAID with no performance benefits (just capacity).

JBOD is spanning 2 or more disks - not RAID... pretty scary stuff, IMHO...

In the Rosehill enclosure terminology, JOBD == Big Mode, normal mode is to have the drives separate - back to OP's question, setting up a cron task to rsync from the source disk to the destination disk is a good approach...

 

[ColinTaylor]

JBOD is spanning 2 or more disks

No it isn't. I think you need to read all the following posts.

In the Rosehill enclosure terminology, JOBD == Big Mode, normal mode is to have the drives separate

Wrong. From the manual:

JBOD: It enables each hard drive to be seen separately as single drives, showing 2 HDD capacities.
BIG: It concatenates a series of physical hard drives as a single large volume

 

[L&LD]

ColinTaylor, I know you're not 100% correct either, but I can live with that.