unRAID SSD options

[DaShesano]

Hi all,

I was hoping to add an SSD to my unRAID server as a cache drive, and also to run VMs off of (I run between 3-5 on a day to day basis). I was wondering about using an intel 910 PCIe SSD and if that would work with unRAID (I know a PCIe drive is overkill) or if I should use a write optimized SSD like the samsung sm863 (240gb).

P.S: I was hoping to use a 240 gig-ish PCIe SSD to free up space in my system so I can use the drive bays for hard drives, but write optimized SATA SSDs will work fine.

Thanks

[ARikozuM]

Please don't.

[Electronics Wizardy]

It will work with a pcie or sata ssd just fine. Id try it without one first as it really won't help much even for the vms.

[xentropa]

I am not sure if I understand your question entirely but I will give you my best input.

 

Regarding RAID for pcie SSDs (that don't use the PCH), I think only software raid is possible since there isn't any hardware support for raid in the CPU.  Software raid MAY be slower than no raid because of the computational overhead on the CPU and memory to stripe the data sent to the pcie ssds, if the PCIe bus isn't saturated (which I doubt).  Unless there is a reason you want to use raid 0 to make a single volume with the capacity of two ssds, I can't say for certain there will be a performance gain using raid 0 on pcie ssds.

 

As for sata ssds, its more plausible that a performance gain can be achieved since raid 0 striping is performed on the PCH and therefore wouldnt put as much load on the CPU or memory. 

[leadeater]

You will be much better off running a dedicated SSD storage pool for anything that you want to be quick or to host VMs on, caching is never perfect. You could use a mirrored pair of Samsung 850 EVO's and a mirrored pair of WD Reds for bulk storage, lower performance or backup of the SSD if only use a single SSD.

 

You won't need a write optimized SSD or server SSD from the description you have given, you have to be doing serious sustained full write utilization of an SSD to ever worry about write endurance. SSD endurance is so high now days the size of them will become irrelevant before they fail due to write wear.

 

I've got 2 840 Pros and 4 850 Pros that I have had for a long time, the 840's for about 3 years, all with between 50TB to 70TB of write wear on them and I can very confidently say I would be stressing mine more than you will. I run mine in my server at home that depending on what I'm trying out at the time could be hosting up to 50 VMs, some of which are write demanding, plus I keep my steam library on it which is about 1.5TB. I also frequently copy all the data off the server, reconfigure it and copy it all back leading to the mentioned 50TB-70TB wear.

 

Quote

Samsung SSD 850 EVO Lifetime Estimation
	120GB	250GB	500GB	1TB
Raw NAND Capacity	128GiB	256GiB	512GiB	1024GiB
NAND P/E Cycles	2,000
Raw NAND Endurance	250TiB	500TiB	1000TiB	2000TiB
Lifespan with 20GiB of Host Writes per Day with 1.5x Write Amplification	23.4 years	46.8 years	93.5 years	187.0 years
Lifespan with 100GiB of Host Writes per Day with 3x Write Amplification	2.3 years	4.7 years	9.4 years	18.7 years

http://www.anandtech.com/show/8747/samsung-ssd-850-evo-review/4

 

Quote

All in all, there should be absolutely no reason to worry about the endurance of the 850 EVO, especially given the endurance ratings Samsung is giving to the 850 EVO (75TB for 120/250GB and 150TB for 500GB/1TB).

http://www.anandtech.com/show/8747/samsung-ssd-850-evo-review/4

 

Remember warranty endurance figures are very conservative as that is what they guarantee and honor a replacement if the product fails before then. SSD last much longer than the warranty figures but even then 75TB or 150TB of writes is a hell of a lot, even for a high demand server workload.