Is it possible ...

[Billped]

I searched the forum and found no such similar questions/answers.  If such a post exists, please point me to it and accept my humble apologies.

 

I am considering an unraid setup, ideally being multiple configurations within a single box, such as:

* 12 drives, one chassis, one mobo, ...

* Two separate arrays of drives (say, two of five drives each)

* Additional non-raid drives (perhaps for simple JBOD backups of the most critical files)

 

Possible?  If so, would this require multiple USB keys?  Also if so, is it a good idea?  Should I leverage the mobo's built-in raid function for the second array instead of using Unraid?

 

Motivation: I would like to have both a media server (the main use) and a general backup capability for my home network and our four (soon to be five) computers.  I would regularly buy larger drives for the media array, then take the smaller drives and move them to the home backup array.  Yes, I could probably have one large array instead, but something tells me that there are benefits to keeping them separate.  The separate JBOD requirement is because I would prefer to avoid having external drives hanging off of the box.  Backups would be during off-hours, so network congestion caused by the multiple uses should be minimized.  I would like to use one box to minimize cost and clutter.

 

A second possible configuration is an 8 drive unraid and two two-drive simple raid 1 configs (one for the general backup, which should be fairly small given that all of the audio and video will be on the larger array, and the second would be the "I am paranoid, aka 'in lieu of tape', backup").

 

Any feedback or guidance would be greatly appreciated.

 

 

Cheers,

Bill

[Koolkiwi]

I am considering an unraid setup, ideally being multiple configurations within a single box, such as:

* 12 drives, one chassis, one mobo, ...

 

Yes, and you can now have up to 14 drives with unRAID V4.0beta.

 

* Two separate arrays of drives (say, two of five drives each)

 

I don't believe it is possible to have multiple array's on the one server at this time.  However, I'm not sure I see what the benefit would be? 

 

Certainly no benefit when reading data, only possibly some performance benefit when writing data to one array while sumultaneously reading from the other (as each array would have a lesser number of drives to calculate parity, on so write performance would be improved etc. and would not involve the drive you were reading from in the other array).

 

However, this would be at the cost of consuming 2 drives for parity and would be questionable whether the simultaneous write / read across 2 arrays benefit would make any practical difference in actual usage?

 

I would suggest perhaps just keeping your "general backup" data on specific drives in the array, seperate to the drives used for your "media server".   This would at least mean that any simultaneous purpose reading would be from seperate drives, and any simultaneous writing would only likely involve a read from the other drive being simultaneously read (as part of the write parity calculation).

 

* Additional non-raid drives (perhaps for simple JBOD backups of the most critical files)

 

This is not currently possible, although it is in the published wish list as "permit some disks to be outside the array" here:

http://lime-technology.com/forum/index.php?topic=266.0

 

[Billped]

I appreciate the thorough reply.

 

I also am not certain about the "multiple arrays in one box" benefit, so let's rule that one out.  I like your idea of merely designating certain drives to be for certain uses.  Not terribly different than segregating movies from music from photos.

 

Re: drives outside the array - yep, that is what I want and I guess I'll just have to be a keen follower of the releases and wishlist.

 

 

Cheers,

Bill

[Koolkiwi]

There is one aspect of my reply above that I would like to clarify with Tom, which may actually negate any possible 'dual use' performance advantage of multiple arrays (when in a normal use non-degraded state).

 

When writing data to a data drive in the array, is it only the parity drive that is also accessed (for a parity read, parity data re-calc, parity write), or are all drives read accessed in the process of updating (and checking?) the parity for new data being written?

 

ie. If only the data drive being written to and the parity drive are active (as I suspect), during a normal (non-degraded state) write of new data, then there would be absolutely no performance benefit in the example I used above - of writing data to one array, while simultaneously reading data from a drive in a second array.

 

The only benefits would then seem to be a performance improvement when one of the array's is in a degraded state, purely due to the individual array's having fewer disks to access in calculating the failed drive's data.  As well as a benefit in the reduced probability exposure to simultaneous drive failure in a single array (by the nature of the array's having less drives).

 

However, whether these benefits are of any significance over the cost of an additional drive being consumed for a second array's parity, is probably highly debatable (and probably something I wouldn't consider worthy of any priority above other wishlist items).

 

EDIT: This question appears to have been answered by Tom in this post:

In unRAID storage organization, bear in mind it's unusual to have more than a couple drives active at a time.  If you are reading a single file then only 1 drive is active, if writing then only 2 are active (data disk + parity disk).

[limetech]

Koolkiwi, your analysis is correct.  During write, only data drive plus parity drive is active (unless the data drive being written is 'disabled' in which case all other data drives are read and only parity is written).

 

Actually having multiple arrays in the same box could be beneficial, especially once SATA port-multiplier support becomes stable.  It might be feasible to have far more than 14 drives controlled by one system.  Added to the Laundry List:

 

- support more than 1 array (parity group) in same system

[Peregrine]

Koolkiwi, your analysis is correct.  During write, only data drive plus parity drive is active (unless the data drive being written is 'disabled' in which case all other data drives are read and only parity is written).

 

Actually having multiple arrays in the same box could be beneficial, especially once SATA port-multiplier support becomes stable.  It might be feasible to have far more than 14 drives controlled by one system.  Added to the Laundry List:

 

- support more than 1 array (parity group) in same system

 

Beauty!

[WeeboTech]

Actually having multiple arrays in the same box could be beneficial, especially once SATA port-multiplier support becomes stable.  It might be feasible to have far more than 14 drives controlled by one system.  Added to the Laundry List:

 

- support more than 1 array (parity group) in same system

 

I see this as beneficial for using with  SANS DIGITAL MS4UM 4 bay eSATA Port Multiplier & USB Enclosure - Retail

http://www.newegg.com/Product/Product.aspx?Item=N82E16816111025

 

[WeeboTech]

Actually having multiple arrays in the same box could be beneficial, especially once SATA port-multiplier support becomes stable.  It might be feasible to have far more than 14 drives controlled by one system.  Added to the Laundry List:

- support more than 1 array (parity group) in same system

 

To add to this...

Here is a potential for 20 drives in eSata format.

 

http://www.sonnettech.com/product/tempo_sata_e4p.html

http://www.sonnettech.com/product/fusion500p.html

 

if I were to use this I might want 4 arrays, one parity drive per array in an enclosure.

 

For my mini itx machine, I've been considering 2 arrays each with an internal parity drive and eSata data drives.