How does unRAID create the multi-sized software raid4?

[Automatic]

I'm currently looking at other programs released and I'm trying to find something that does something like unRAID, however, I can't seem to find any program (like MDADM) that allows raid 4 arrays (With or without striping) to have multi-sized disks.

 

So, how does unRAID do it? Is custom? Is there anything like it I can use that's not unraid?

 

I know I could probably find out by spending hours going through my unraid box, but, I'd prefer to save those hours.

[sacretagent]

DROBO 

 

expencive but seems pretty similar to what unraid does...

[Automatic]

DROBO 

 

expencive but seems pretty similar to what unraid does...

 

That's a piece of hardware, right (Google results return hardware)?

 

If so, I'm looking for software to throw on my already existing linux setup.

[Ford Prefect]

..not raid-4 in any sense...

 

... but for win and with pooling of drives with mixd sizes, I am using Stablebit DrivePool quite succesfully.

Parity I then do offline with snapraid.

[vl1969]

Well linux with btrfs+lvm works similar. And you can have raid 5 or 6

 

Sent from my SGH-T889 using Tapatalk 4

 

[sacretagent]

Well linux with btrfs+lvm works similar. And you can have raid 5 or 6

 

Sent from my SGH-T889 using Tapatalk 4

 

but no disks spinning down when not in use...

[garycase]

UnRAID is not RAID-4, as it does not stripe the data.    It does, like RAID-4 use a dedicated parity disk ... but the similarity basically ends there.

 

I'm not aware of any other system that allows an arbitrary mix of drive sizes like UnRAID.    If you want that feature, it's probably the only choice.

 

[c3]

I can see how you might call unRAID a RAID4, but as it is named unRAID, it's not RAID. RAID definitions are block level, under the filesystem. unRAID and others are filesystem or higher. What makes this important is the contents of any file is stored on a single disk, so the data loss is always files, never part(s) of files. Or anything left is still whole

 

There are several other product/packages "in this space" which you'll have to set your boundaries, depending on your expectations and ability to execute; Microsoft Storage Spaces, FlexRAID, SnapRAID, drobo, synology, Thecus, btrfs, FreeNAS, OpenFiler,  OpenIndiana, OpenMediaVault, NAS4Free, ... all the way up to things like OneFS, OnTap, Cinder, CleverSafe.

 

While Drobo and others are "hardware", they still run software. The hardware in most cases is rather uninteresting. The software has similarities to unRAID, as many are running linux and most the rest are BSD.

 

Lastly, how does unRAID do it? This is the software you license from Lime-Technology, and that license does not include how. If this is your interest, you should read up on FUSE

http://en.wikipedia.org/wiki/Filesystem_in_Userspace#Example_uses

 

 

[vl1969]

Well linux with btrfs+lvm works similar. And you can have raid 5 or 6

 

Sent from my SGH-T889 using Tapatalk 4

 

but no disks spinning down when not in use...

 

I am sure you can spin-down the disks when not in use.

the only issue is when you reading/writing to array all disks are spin up where in UnRaid only disk it is writing/reading from is spin-up thus save power etc.

for me it would not be that important though but YMMV

[drawz]

Synology and Drobo handle different sized drives by using smaller partitions as needed.

 

For example, if you have 500GB, 2TB, and 3TB drives, you will have a 500GB partition on each drive joined together in a RAID 5 array. A 1.5TB partition on each of the remaining drives are set up as a RAID 1 array. The last 1TB on the 3TB drive is unused. The two arrays are joined together to look like one big disk.

 

The software to deal with all this with a reasonable user interface is their secret sauce and varies slightly. Synology Hybrid RAID is LVM/mdadm under the hood. Drobo is proprietary.

 

As noted above, unRAID differs from other RAID setups in that it does not stripe data across drives. This fact is what allows files to reside on a single disk, and in turn not spin up the whole array for every access. This is also what allows individual data disks to be removed from an unRAID server and be read individually on any system that can handle ReiserFS.

 

I'm not sure how to create an unstriped RAID 4-like array, but I believe unRAID does it with standard linux tools. Once again, the user interface to deal with all this is the secret sauce. To my knowledge, and I have also looked, there is nothing else out there that does anything like this out of the box with a reasonable UI.