Hello,

 

If none of your drives are big enough to be parity, can you have multiple parity drives or even multiple arrays?  For example, say you have 4 drives but neither of them is large enough to be parity for the other 3.  Can you use 2 of them as parity or create more than one array on the unRAID server?

 

TIA>

-g

As far as I know, you cannot do that currently.  At least, you cannot do that within unRAID. 

 

I don't know whether given a hardware RAID controller, you could JBOD a couple of disks and have them/it recognized in unRAID.  I think that would depend on whether or not unRAID has the drivers to recognize that controller.

 

Multiple arrays is currently a "No."

It's on the "laundry list" but I was told it's not coming soon.  Of course I defined soon as within the next week, so who knows.

 

There is a way to do it, but unless you have the right equipment laying around it won't be worth it.  You need to have an eSATA port on your motherboard (if you don't have that and can't afford a true eSATA port, you can get an adapter plate that basically just plugs into a regular SATA port on your motherboard).  You also need an external SATA enclosure that supports RAID-0.  Put your two smaller SATA drives in that, and use the configuration software that came with it to set it up in a RAID-0 array.  Now plug that all up into your unRAID server, it should see it as a single drive.  So if you have two 500GB drives, it will be reported as a single 1TB drive.  No special support is needed via linux or unRAID, as far as it's concerned only one drive is connected.

 

Wish I could help you out with the hardware, but all I have is an external enclosure with USB only (it works exactly the same otherwise, but reading and writing to a parity drive over usb would be just a tad slow).  The one I have with usb and eSATA is currently connected to my HR20, the HR20 can only see one external drive, and with two 1TB drives in RAID-0 it's reported as one large 2TB drive.  Works fine.  You'd probably pay $150 or so to get such an enclosure, or you can just buy one with drives already in it for not much more than the cost of the drives alone (at the time I bought mine it was $500, and the 1TB drives would have cost about $230 each, so that's about $40 extra for the enclosure).  Mine's a Cavalry unit, but others should work too.

I don't know whether given a hardware RAID controller, you could JBOD a couple of disks and have them/it recognized in unRAID.  I think that would depend on whether or not unRAID has the drivers to recognize that controller.

 

If you have the right controller supporting port multipler, and the right hardware or hardware processor(SIL-5744) it's feasible to STRIP or SPAN two drives. For the cost of that, it may be better to just by a new hard drive.

 

I tested this out the other day using a SIL-3124 SATA port and an external SIL-5744 Hard drive array.

I suppose you could do the same internally with a SIL-5744 bridge board mounted internally and a SATA-ESATA adapter.

(I plan to do this).

 

Here is some information with my tests.

http://lime-technology.com/forum/index.php?topic=1750.0

 

It did work, then again, for the $129 I could have bought a 750GB hard drive.

in my case, I plan on using the SAFE33 mechanism to get the best of both worlds.

 

 

and another device that will probably work.

http://www.caloptic.com/cgi-bin/quikstore.cgi?product=ezRAID3&detail=yes

 

and another device that could be rigged with a few cables.

http://www.cooldrives.com/usb20espcbfo.html

 

I.E. an internal SATA cable to external ESATA port, an eSata cable, briidge board and some mounting.

At least that is how I may end up doing it to keep everything self contained.

 

 

I think the problem with JBOD, is often times the enclosure requires a port multiplier for that to work.  If you get one that supports RAID-0, then it should be reported to the OS as a single large drive, least that's how it works with mine.  No need to worry about whether your eSATA port (or regular SATA if you simply use an adapter) supports PM or not.  Plus since it's a parity drive we're talking about and not a data drive, I don't think there's a difference, if one drive goes you've lost your parity but no data.  If this was for a data drive then I'd want to go JBOD, less chance of data loss.

 

If your eSATA port does have PM support, I'd probably try RAID-0 first, I think it'd give you less problems.  If for some reason that didn't work, then try JBOD.

 

Edit:  I can think of one reason you'd prefer JBOD over RAID-0, it may only need to spin up one drive when reading/writing parity.  You'd need to make sure the enclosure only reports this as one drive to the OS, if it reports as two then I don't think it'd work.

Agreed, if you get a hardware only device, then you would not need port multiplier technology.

The device I presented can do both.

 

RAID1, RAID0, STRIPE, SPAN  whereby the host will see 1 drive.

If yout want something special like SAFE33/SAFE50 or 2 JBOD drives, then you need a port multiplier aware SATA port.

The host will then see two drives.

 

And yet another link showing the bridge board with more descriptive information.

Keep in mind, this would be something "rigged" LOL. unless you put it in an external enclosure designed for the drives.

 

WeeboTech <-- Good a rigging things  LOL!!

Thanks for the replies...

 

So if I were to JBOD a couple of drives (or more) and use that as my parity, what would happen if one of the drives in the JBOD array failed?

Thanks for the replies...

 

So if I were to JBOD a couple of drives (or more) and use that as my parity, what would happen if one of the drives in the JBOD array failed?

 

I think you'd want it setup as RAID-0, or just whatever would let unRAID see it as just one drive.  Regardless, if one of the drives failed, then you'd basically not have a parity drive.  Just replace the dead drive, make sure the RAID-0 or whatever is setup correctly, then reconnect to unRAID and let it rebuild parity.

 

You'd basically be doubling your chances of the parity drive failing.  If you're having to buy all this equipment to get it to work, then your money would be better spent just getting one large drive to use as parity, and you can still use your smaller drives for data.  If you already have the equipment, then go ahead and use it.

 

I was thinking about it, and even a usb-only enclosure might be somewhat tolerable.  Write speeds are slow anyways because parity has to be calculated.  Read speeds shouldn't be affected unless you're reading from a dead/missing drive.  I haven't actually tried this out though, so I don't know what the performance hit would be in the real-world.  If all you have is a usb enclosure, might be worth a shot.  Just post some of your read and write speeds so we can tell if they're halfway decent or not.

f you're having to buy all this equipment to get it to work, then your money would be better spent just getting one large drive to use as parity, and you can still use your smaller drives for data.

 

This is what I mentioned before. The cost of an external RAID-0 capable unit vs the cost of a drive has to be weighed.

Then you have to add in the complexity of the setup and your time.

 

The device I presented will work as you would like for $149 + shipping. (plus any cables) providing you have a spare sata port.

 

it would be nice if unraid did the spanning internally. Maybe it will be a future feature. (hope so!).

In the meantime if you are serious about going down this route then do a cost analysis.

 

hardware + cables + time vs new larger drive.

 

 

I have one of these for PATA drives.

 

AMS VENUS T4U DS-2340UBK 3.5" USB 2.0 External Enclosure - Retail

http://www.newegg.com/Product/Product.aspx?Item=N82E16817332008

 

It's neat, It's USB, although I have not tried it with unRaid or as a Parity drive..

Maybe I'll get a chance to hook it up this weekend.

 

If you want to go this route, then I would still recommend the other DS-PRO unit. It does USB and eSata.

I have not tested USB on it yet though. We'll see this weekend.

 

 

f you're having to buy all this equipment to get it to work, then your money would be better spent just getting one large drive to use as parity, and you can still use your smaller drives for data.

 

This is what I mentioned before. The cost of an external RAID-0 capable unit vs the cost of a drive has to be weighed.

Then you have to add in the complexity of the setup and your time.

 

The device I presented will work as you would like for $149 + shipping. (plus any cables) providing you have a spare sata port.

 

it would be nice if unraid did the spanning internally. Maybe it will be a future feature. (hope so!).

In the meantime if you are serious about going down this route then do a cost analysis.

 

hardware + cables + time vs new larger drive.

 

 

 

Exactly.  $150 to use two smaller drives as a parity drive which has double the chance of failing, or $180 for a 1TB drive (keep an eye out, you'll find deals pretty regularly) which has got to be at least as large as your current largest drive, plus you can use the smaller drives for data.  Someone like me can just dig through their boxes of junk (as my wife calls it) and possibly find just what you need.  Otherwise, just get a new larger drive.

 

Of course I should point out that having two drives serve as a single parity drive isn't as bad as it sounds.  While there is a better chance that the parity drive will be out, what would happen if both of those drives failed at the exact same time?  If they are serving together as a parity drive, in essence you've only lost one drive (they're working together to be one drive, doesn't matter if one or both go out).  If they are working as data drives, then you've lost all the data on those two drives (unRAID can only recover from the loss of any one single drive, not two).  So don't be TOO scared to do it your way, if it's feasible.

I was thinking about it, and even a usb-only enclosure might be somewhat tolerable. Write speeds are slow anyways because parity has to be calculated.

How about a firewire enclosure instead? I've found external firewire hard drive enclosures to be quite a bit faster than USB 2.0.

 

This is what I mentioned before. The cost of an external RAID-0 capable unit vs the cost of a drive has to be weighed.

Then you have to add in the complexity of the setup and your time.

 

The device I presented will work as you would like for $149 + shipping. (plus any cables) providing you have a spare sata port.

 

it would be nice if unraid did the spanning internally. Maybe it will be a future feature. (hope so!).

In the meantime if you are serious about going down this route then do a cost analysis.

 

hardware + cables + time vs new larger drive.

Right, I understand in the end it might not make sense due to cost. I haven't committed to buying/building an unRAID server just yet. Just exploring my options because in the near future (probably later this year) I'll need reliable mass storage. I've been getting by with a couple of external firewire enclosures and just upgrading the drives as needed and using software to backup one drive to the other but eventually that's not going to cut it.

 

So without addtional hardware for the "workarounds" mentioned above, basically the best one can hope for with an unRAID server is 1TB of data since the largest single drive (for parity) available today is 1TB, right?

basically the best one can hope for with an unRAID server is 1TB of data since the largest single drive (for parity) available today is 1TB, right?

 

Wrong... one parity drive can protect any number of data drives. 

unRaid can currently handle 16 drives in its array.  One parity and 15 data.  So unRaid is "limited" to 15 Terabytes using 1TB drives.

 

Joe L.

basically the best one can hope for with an unRAID server is 1TB of data since the largest single drive (for parity) available today is 1TB, right?

 

Wrong... one parity drive can protect any number of data drives. 

unRaid can currently handle 16 drives in its array.  One parity and 15 data.  So unRaid is "limited" to 15 Terabytes using 1TB drives.

 

Joe L.

Maybe I misread the requirments.  I thought I read somewhere that the parity drive has to be greater than or equal to the data drives?

$180 for a 1TB drive (keep an eye out, you'll find deals pretty regularly)

 

Hmmm... pls post to the deals forum if you see that again!

 

basically the best one can hope for with an unRAID server is 1TB of data since the largest single drive (for parity) available today is 1TB, right?

 

Wrong... one parity drive can protect any number of data drives. 

unRaid can currently handle 16 drives in its array.  One parity and 15 data.  So unRaid is "limited" to 15 Terabytes using 1TB drives.

 

Joe L.

Maybe I misread the requirements.  I thought I read somewhere that the parity drive has to be greater than or equal to the data drives?

Greater than, or bigger than the biggest of your data drives... not bigger than the total capacity of all your drives.

 

In theory, a single parity drive could protect 1000 data drives.  Problem is, to reconstruct a single bit, you must read all 1000.  16 drive limit is because of power supply issues, bus bandwidth issues, controller card issues, server case issues, etc. (actually unRaid handles 17 drives as of this week, but the 17th drive is used as a cache, not as part of the array)

Maybe I misread the requirments.  I thought I read somewhere that the parity drive has to be greater than or equal to the data drives?

 

now that would be an interesting total failure as a product

I am not even sure how it would work... one disk with parity and the rest unprotected? or a "parity" for each disk? (so multiple RAID1 arrays...)

 

if I read the requirements like that, I wouldn't even spend 10 more seconds to look at the site

 

(no offense - just found your interpretation very interesting)

 

 

Greater than, or bigger than the biggest of your data drives... not bigger than the total capacity of all your drives.

 

In theory, a single parity drive could protect 1000 data drives.  Problem is, to reconstruct a single bit, you must read all 1000.   16 drive limit is because of power supply issues, bus bandwidth issues, controller card issues, server case issues, etc. (actually unRaid handles 17 drives as of this week, but the 17th drive is used as a cache, not as part of the array)

Sorry, I misread it.

 

In that case wouldn't the ability to house multiple arrays under one unRAID server be a rather important/desireable feature since 16 drives in an array must be rather risky?  Anyone actually have a 16 drive array?  What's the chance of losing multiple drives at once or in a relatively short time frame?

now that would be an interesting total failure as a product

I am not even sure how it would work... one disk with parity and the rest unprotected? or a "parity" for each disk? (so multiple RAID1 arrays...)

 

if I read the requirements like that, I wouldn't even spend 10 more seconds to look at the site

 

(no offense - just found your interpretation very interesting)

I'm not a storage expert that's why I'm spending the time to have a look well before I even need to make a purchase.  And that's why I registered and posted questions.

basically the best one can hope for with an unRAID server is 1TB of data since the largest single drive (for parity) available today is 1TB, right?

 

Wrong... one parity drive can protect any number of data drives. 

unRaid can currently handle 16 drives in its array.  One parity and 15 data.  So unRaid is "limited" to 15 Terabytes using 1TB drives.

 

Joe L.

Maybe I misread the requirments.  I thought I read somewhere that the parity drive has to be greater than or equal to the data drives?

 

The parity drive must be the largest individual drive.  You can have any number of data drives (up to the 15 data drive limit) the same size or smaller than the parity drive.

I'm not a storage expert that's why I'm spending the time to have a look well before I even need to make a purchase.  And that's why I registered and posted questions.

 

nothing wrong with that man

 

I am just curious on how would a concept like that would be even remotely useful (this is not related to storage expertise, I mean as a concept)

 

edit: forget it... I get what you thought... but then indeed the "array" total would be as large as the parity (currently 1TB)... why wouldn't someone then just buy two 1TB disks, mirror them and spare all this fuss building a dedicated machine for that (or buy any of the many 2-disk NAS out there)

 

 

 

In that case wouldn't the ability to house multiple arrays under one unRAID server be a rather important/desireable feature since 16 drives in an array must be rather risky?  Anyone actually have a 16 drive array?  What's the chance of losing multiple drives at once or in a relatively short time frame?

 

I'm not a statistician or even very scientific in this response, but I think with today's quality drives, it's not as risky as you might think.  I'd bet a lot of drive failures with newer disks would be due to some batch-specific manufacturing issue, so you might want to stagger your drive purchases (or purchase from multiple vendors) just so you don't get drives that were built in the same batch. 

 

Additionally, with the way that a lot of us use our machines (serving entertainment media), the disks are spun down a lot of the time.  I recently sold some 300GB and 500GB drives when I consolidated 2 unRAIDs down to 1 using 1TB drives.  I did some S.M.A.R.T. tests on the drives that I was selling (so I'd be able to show the buyers that these were quality drives), and even though the unRAID had been on for months on end, the drives had low hours of Used Life because they had been spun down most of the time (I think I'm reading this correctly).

 

Another reason for me choosing unRAID over RAID5, is that when/if you do have multiple drive failure, you only lose what was on the failed disks.  With RAID5, you'd lose everything.  Again, most of my data is entertainment media.  I can re-rip if needed...it'll take time, but it's replacable.  Plus, I have less chance for having to replace EVERYTHING versus just a portion.

 

  What's the chance of losing multiple drives at once or in a relatively short time frame?

There's a whole thread discussing that very topic. 

See here...

http://lime-technology.com/forum/index.php?topic=1751.msg12170#msg12170

 

Best estimate is somewhere around 15-20 years before two drives would fail at the "same time" in a 12 drive array. (the "same time" defined as being within the 128 hour window of time within which a drive is determined to be defective, replaced, and rebuilt from the others.)  If the MTTR (Mean-time-to-repair) is better than 128 hours, your reliability improves accordingly.  Also, I would guess that 20 years from now, these 1TB drives will seem tiny.

 

Also... there are RAID arrays where every disk is mirrored with a copy of that data on another equal size drive.  That is not parity, but mirroring.  It is known as RAID-1.  It is used occasionally, especially if there are only two drives (with one data, the other to provide redundancy/backup)

Joe L.

Another reason for me choosing unRAID over RAID5, is that when/if you do have multiple drive failure, you only lose what was on the failed disks.  With RAID5, you'd lose everything.

  Yup that's definitely one reason why I decided to look more closely at unRAID.

 

Again, most of my data is entertainment media.  I can re-rip if needed...it'll take time, but it's replacable.  Plus, I have less chance for having to replace EVERYTHING versus just a portion.

That's the catch for me, most of the data I'd be putting on an unRAID system would be irreplaceable.

Maybe I misread the requirments.  I thought I read somewhere that the parity drive has to be greater than or equal to the data drives?

 

Ah, here's the confusion!  The parity drive has to be as big or bigger as THE largest data drive.  If your data drives are 250GB, 300GB, and 750GB, then the parity drive must be at least 750GB if not larger.  The only thing to worry about is if you have multiple drives with the same capacity from different manufacturers.  Sometimes there are slight differences, so a 1TB drive from Western Digital may be a few megs smaller than one from Maxtor (or vice versa).  Someone with multiple 1TB drives from multiple manufacturers will have to chime in about that.  It's not really that big of an issue, if your new data drive turns out to be a tiny big larger than the parity drive, just unassign the parity drive, make it a data drive, then add the new drive as a parity drive.

 

As far as firewire enclosures, I don't think the unRAID kernel has firewire support.  Feel free to compile it in, but no guarantees it'd work.

 

Edit:  Man, I was beaten bad by this one...so many replies before me?  I thought I had refreshed before I posted, obviously not.  Oh well.