Hi,

 

I'm new to unRAID. I was wondering if I could buy something like an IBM M5015 and have a RAID6 array alongside unRAID on the same controller? If this isn't compatible then can anyone recommend a controller that is compatible please?

 

Also I've heard of people using two disks for parity but I can't find any information on this. Are they just creating a RAID1 mirror and using that as a parity device or are they using two separate disks?

 

Thanks,

 

Joe

You can't use a RAID array "alongside" UnRAID.    If you want a RAID-6 array, just use the controller with another OS and create it.

 

As for dual parity for UnRAID => this is an often-requested feature; but has not been implemented, and there's no schedule for when (or even if) it will be added to UnRAID.

 

Several people run cache drive on RAID 1 and parity on RAID 0 using Areca controllers.

Several people run cache drive on RAID 1 and parity on RAID 0 using Areca controllers.

 

Interesting => I knew some used RAID arrays for cache drives; but wasn't aware you could assign a RAID array as one of the disks "in" the actual UnRAID array.    If you can do it with parity, I'm sure you can do it with other drives as well.

 

So with enough RAID controllers, you could create a bunch of RAID-1 arrays, and use each of those as a single "disk" in UnRAID !!      ... THAT would be some serious redundancy !! [At the "cost" of  (2N + 2) disks to get N disks worth of storage.]

 

... but it would also take a minimum of 4 disk failures to lose any data (and probably even more, as to lose data with 4 failures would require that those 4 disks were all part of the same 2 RAID-1 arrays)

 

Sound interesting, so is it only Areca controllers? Any particular models? The way I understand it is unRAID uses block devices and a block device can be a disk, RAID volume, loopback device etc etc.

 

Joe

I assume it's with any hardware controller that doesn't require OS drivers ... Areca, LSI, Adaptec, etc.

 

As I noted above, I knew folks were doing this for cache drives; but hadn't really thought about using them for members of the UnRAID array.  But it makes sense -- as long as it's a "drive" to the OS, it simply doesn't matter what the physical characteristics are of that "drive".

 

Interesting indeed.

I wonder how this would work with temp reading, SMART, spindown and suchlike.

If anyone doing this cares to post, that'll be helpful!

I was wondering the same thing -- I suspect they simply wouldn't work [unless the RAID controller itself had spindown enabled].

 

The reality is I can't really think of a good reason to do it that way => perhaps a RAID-0 for cache for performance reasons (although an SSD would be better yet).

 

But if you want a RAID-6 array, then just use a hardware controller that supports it -- no need for UnRAID.

 

I can think of a lot of reasons NOT to do it ... the "parity drive" now has to be as large as the largest component array;  spindown, SMART, temperature readings, etc. won't work;  you'll need a Linux add-on that provides RAID status for the component RAID arrays;  etc.

 

I'm going to have a RAID1 parity disk when I build my rig in a couple of months so I can do some testing then. This should also eliminate my need for RAID6 since I will have dual parity anyway.

 

Some of the more expensive RAID controllers can pass through things like SMART and possibly temperature reading but HDD spin down would have to be handled by the RAID controller and unRAID probably won't be able to touch it. (You wouldn't want it to since it doesn't know what has been buffered in memory or written to disk and you could cause all sorts of issues by forcibly spinning disks down.)

 

Joe

 

EDIT: Didn't see your message garycase, what I'm proposing is:

 

2x4TB disks as a RAID 1 array - this is the parity drive

1x4TB normal unRAID drive

various other disks I'll chuck in as normal unRAID drives

 

Would lack of temperature reading, SMART and disk spin down control cause huge issues?

I'm going to have a RAID1 parity disk when I build my rig in a couple of months so I can do some testing then. This should also eliminate my need for RAID6 since I will have dual parity anyway.

 

NO -- you won't have dual parity !!

 

You'll have a mirrored parity disk; but you'll still lose data if two disks fail UNLESS one (or both) of those disks are members of your parity disk array.    This is not even close to dual-parity !!    The ONLY combinations of two-disk failures you could sustain in that arrangement is if both of the drives in the parity array failed;  or if one of the drives in the parity array and one other drive failed.    ANY other combination and there's no difference from a "normal" UnRAID setup.

 

... AND unless you have some means of monitoring it separately, if one of the disks in the parity array failed, you wouldn't know it from the UnRAID status screen, as it would still think the parity drive was okay.

 

Ah, yes your right it wouldn't. I think it might still be worth doing though since the parity drive tends to be biggest and used the most (for writes at least) so I'd guess that it would be the most likely to fail (Is this the case normally?)

 

Joe

Ah, yes your right it wouldn't. I think it might still be worth doing though since the parity drive tends to be biggest and used the most (for writes at least) so I'd guess that it would be the most likely to fail (Is this the case normally?)

 

Joe

 

Nope. Disks are meant to be used. Power-on hours is the only real measure. RAID 0 parity gives substantial write performance improvement with multiple writers.  RAID 1 parity get you almost no additional protection. RAID 1 cache protects the cache contents. A SSD cache is nice because you can run the mover very often without affecting write performance. But since the network is the bottleneck a large RAID 1 cache is generally a better choice. If your running 10Gig Ethernet then you can afford a RAID 1 SSD cache with the mover running at high frequency. YMMV with usage pattern.

Agree with dgaschk => if you're going to add a RAID array on top of UnRAID, use it for the cache drive.  That's the weak point in an UnRAID setup, since the cache isn't fault-tolerant.  Using a RAID-1 array for that would resolve that.    In fact, UnRAID v5.0 WAS going to provide for that capability ... but it was withdrawn from the features that made the release.    Hopefully it will be a feature of a relatively near-term "point" release (e.g. v5.1) ... but there's no guarantee of that.

 

As for the parity drive being the most-used drive => in general, that's probably not true.  It's certainly used for EVERY write;  but is NEVER used for a read unless the array is degraded (i.e. has a failed disk) ... in which case EVERY drive is being used.

 

Ah I understand now. It will be a few months before I gather all the kit together to actually build this box so in the mean time I'll do some testing in VMs and figure out what I want to do.

 

Thanks,

 

Joe

I though I put in my 2c.

 

if you want this kind of redundancy and protection, just build the server on something else using Raid-6

you can use NAS4Free with ZFS ,RedHat with ZFS , snapRaid with Linux software Raid -6 on any distro.

 

even better if you are feeling adventures, you can get OpenSuse 12.3 or later and use BTRFS with Raid-6

Raid-6 was added to openSuse btrfs implementation with 12.3 release.

on all that you can mimic the unRaid shares functionality with LVM + SAMBA.

(obviously I did an extensive research on this  :-P )

 

also obviously this setup is  not for noobs(although I am about to try to do this for sh#%s and giggles).

but if you want to use Raid with UnRaid you could not possibly be a noob :-D

 

 

 

I use a HW (Areca ARC-1882) RAID controller, with RAID0 cache drive, and RAID0 parity.  I work with some very large files and databases, and need very high speed access.  (My main workstation has a 6-drive SSD RAID-0 also on an an Areca caching controller.)

 

I back up workstation data to unRAID, and I backup "important" stuff off of unRAID.  Everyone should.  But few people need to backup "everything."  There is a point of diminishing returns.  Hell, I intentionally wipe out and reinstall my OS and all apps on my main workstation once a year.

 

So important stuff is backed up.  Unimportant stuff can be replaced (such as re-ripped)... it is a question of time to do it combined with the likelihood of needing to do it (i.e. 2-drive loss), versus the cost of backing the crap up, storing it, restoring it, and the time to do it regularly.  My personal comfort zone is 2 data drives get backed up regularly, a few individual directories get backed up very frequently, and everything else is hanging in the wind.

 

One of the main (and often under-appreciated) benefits to unRAID over striped RAID is recovery from non-failed disks in a disaster.  Striped RAID, if you have a disaster, EVERYTHING is gone.  Sure you can do RAID6, but if you lose 3 drives, you lose EVERYTHING... with unRAID, you don't.  Non-failed drives can simply me moved to another machine and copied.

 

unRAID is slow to write.  So a striped 4-spindle of inexpensive medium speed drives works fine for cache and "high-speed" data and will do 300MB/sec on 10GigE.

 

unRAID's bright spots are high-flexibility expansion, low cost (high data-to-parity density), high-availability (tolerates 1-drive failure), and disaster recovery/portability for non-failed drives.  Most shortcomings w/r/t speed can be solved by adding striped HW RAID for cache.  Using HW RAID-1/5/6 underneath a data drive give you higher fault tolerance, but at a HUGE cost.... you lose some of the easy recoverability (portability in particular) by using striped RAID underneath a data drive.  You tremendously decrease the data-to-parity ratio and increase costs.  And you backup costs remain the same .... you still have to back up the same "important" stuff even with RAID6 (although some data may be reclassified as less important when on RAID6, but in reality, not that much IMHO).

 

If unRAID is a server you use, leave striped HW RAID for cache, and possible parity.  If you have a need for high-speed storage, consider HW RAID for cache, not for data drives underneath unRAID.  If you need LOTS of high-speed data, more than you want to put on a cache drive, then unRAID probably ain't for you (but it likely makes a great place to backup all that high-speed data).