Finalizing my plans for my first UNRAID storage server (almost exclusively for media) based on the following parts:

 

Norco 4220

Supermicro X8SIL-F

Processor (undecided i3-530 or x3430--yes total overkill but potentially repurpose in future)

Corsair 750 PS (or perhaps an older 500w Seasonic depending on what the 12v says)

WD Green 2TB for parity

A whole box full of dozens of drives ranging from 250GB to 1.5TB.

 

My big question at this point is should I be considering a cache drive?  What speeds should I expect with vs without?  I even have a spare 300GB Raptor I could spare to be a cache drive though I doubt it would make a huge difference based on my understanding (which may be totally wrong btw! ).  I'm planning on migrating ~10TB of data from my current Readynas and WHS servers to the new Unraid box.

 

Thanks for any and all advice!

First, some light reading:

 

To cache drive or not to cache drive?

 

Your Raptor may actually work very well as a cache drive, though I've never tried one myself.  If it is faster than the SSD I tried, then you may set the new record.  Please record it if you do!  A screenshot of a file transfer is fine.

 

Personally, I love cache drives.  However, many users choose not to use them.  It is really a matter of personal preference.

 

Also, I would definitely go for the i3.  It is the ideal unRAID CPU at the moment - low power usage, yet very powerful.

 

Finally, a Corsair 650W PSU should be able to handle a 20 drive array of any configuration.  However, if you prefer the 750 that's fine too.

 

Very nice motherboard, it will suit you well.

What speeds should I expect with vs without? 

Most people get between 25 and 35 MB/s without a cache drive.

With one they get between 50 and 70MB/s.

I even have a spare 300GB Raptor I could spare to be a cache drive though I doubt it would make a huge difference based on my understanding (which may be totally wrong btw! ).  I'm planning on migrating ~10TB of data from my current Readynas and WHS servers to the new Unraid box.

 

Thanks for any and all advice!

At best it would cache the first 300MB, then the rest would not be cached but written directly to the array.  The cache drive is not likely to be very helpful in the initial migration of 10TB.

I thought that when the cache drive fills the writing stops, i.e., fails. Writes will fail once the cache is full. After 300MB the writes will not start going directly into the array.

 

For the initial migration a cache drive should not be used unless it is large enough to hold the entire data set. That is not possible in this case. The cache drive can be activated after the migration.

I thought that when the cache drive fills the writing stops, i.e., fails. Writes will fail once the cache is full. After 300MB the writes will not start going directly into the array.

There is a min free space configurable variable for the cache drive.  If there is that minimum space available it will start writing to the cache drive.  If the drive runs out of space (because the min-free is set too small or set to 0, then the write will fail.  It should be set to a value large than the largest single file you write to the array.  For normal DVD ISO images, something around 10Gig would work.  For Blue-Ray images, probably 50Gig would be better.

 

Once that value is set, if insufficient free space is available in the cache drive the writes will be made directory to the unRAID array.

For the initial migration a cache drive should not be used unless it is large enough to hold the entire data set. That is not possible in this case. The cache drive can be activated after the migration.

Very true.  It will be next to useless in this case of transferring 10TB in the initial load of the unRAID server.

I think you've made more than a few of us jealous with your new unRAID plans.

 

First, i3-530 or x3430. I personally would make this choice based on two things: How important ECC memory is to you, and which will consume the least amount of power. The i3 for power consumption, the Xeon for ECC. I would throw the G6950 into the mix, it is slightly cheaper than the i3-530, and should save a watt or two at idle.

 

I use a cache drive, not to cache my writes, but to run SABnzbd, and to use as a spare in an emergency. I like having parity protection immediately on my data. Since your case "only" holds 20 drives, you will be limited to 18 data drives with a cache drive and 19 data drives without. If you have the budget to seriously consider a x3430, I would take a hard look at the 4224.

 

I would think twice before throwing in a 250G. drive. It will consume more power, increase parity check times and probably has a lot of hours on it, time to send it to hard drive heaven. With drive prices where they are, and the reliability benefits of minimizing spindle counts, I would suggest saving some budget for a couple of 2T. drives.

I use a cache drive for things like sabnzbd and sickbeard.

 

I have the same motherboard and went with an x3430 so i could use the ecc capability of the ecc memory you *have* to use.

 

Having said that, if I was to do it again I'd probably get the x3440.

 

If you look on http://www.cpubenchmark.net/cpu_list.php an i3 is ranked at 159, the x3430 is ranked 117, but the x3440 is ranked at 41 which is impressive! Both the xeon processors are quad core but the x3440 has hyper threading as well.

 

*edit* I should clarify, I'm not saying between an i3 and the x3440 you should get the xeon, I'm saying when I committed to buying the xeon, I did so knowing the xeon was a LOT more expensive than the i3, whereas the step up to the x3440 was relatively small, so if you decide to go the cheaper route I'm sure you will be happy with the i3, but if you decide to go the xeon route think about the x3440 over the x3430 (not that the x3430 isn't a superb CPU)

I have a cache drive but more to store my tv recordings for short term that I don't need parity for. I find only slightly slower going straight to the array.

Josh

Thanks Raj for the link to that thread---VERY useful and didn't find it before with a search.  

 

I ended up buying a G6950 as my local Fry's had it for 90 and the 530 was at 129.  I couldn't be patient and just buy online--had to have it now!

 

I learned my lesson the hard way because the RAM I was planning on using for the motherboard was a 4GB ECC Registered DIMM I had lying around and ECC-reg wont work with a non-xeon cpu.  Ended up finding a thread here which linked a crucial module and ordered that one.  I'm anxiously awaiting its arrival today!

 

I don't see myself moving all 10GB at once but rather slowly migrating to unraid so I think the cache drive will be helpful.  At least it'll give me an excuse to test it out.  

 

My thanks to all for the feedback!!!

From my experiments when you have a cache drive your write speed is defined purely by the performance of your cache drive (assuming your source location is as fast and assuming your cache drive isn't full). The way it works is just a plain write to the cache drive.

 

So basically if you use a modern SATA drive you should see anywhere from 80 MB/s to 120 MB/s sequential writes on large files and that is defined by what drive you pick. I was able to achieve those speeds by transferring a couple GB file. Once I disabled the cache my transfer speeds were 30-50% of the speed of the drive in the array - 30-35 MB/s.