Thanks for the tip. I will try to check it out.

GregoryOrme
Thanks for the tip. I will try to check it out.

I have been reading some reviews and the SM951 works properly in x16 slots for PCs. Is there a problem with OS X with this SSD? I don't have Bootcamp to test if Windows initiates it at full speed.

I would think the only way to test that would be to do what you just suggested and see how it responds with Windows. I don't know anyone who has tried that. I am not running Windows on the Mac; I have a Dell that I use to run Windows.

RAID

macprouser

GregoryOrme

macprouser
Hi again.
Regarding the above, I have discovered the problem after a long process of trying every kind of configuration, benchmarking and observation. The answer was staring at me all the time in the System Profiler.
 
The SM951's on chip controller cannot negotiate a full speed link in a Mac Pro's x16 slot. It can do so in the x4 slot. The XP941 however can negotiate a full speed link in any slot. So until a firmware upgrade ever comes out you cannot create a full speed raid with two SM951s. The best you can get right now is 1500 MB/s read and write.

To make a faster RAID you can either configure a RAID from two XP941s, stripe an XP941 and SM951 together (for some reason slower than the first option), or the best option I had was to stripe an XP941 with two SM951s for 2300 MB/s read / 2100 MB/s write.

macprouser, regarding your third setup, was the SM951 in slot 3, with the two XP941s in slots 2 and 4? I know we are just testing, but in the real world, I don't know that it would be worth it to give up that other slot for 2300/2100 if you were getting the 2231/1750 BareFeats reported with the XP941s in RAID 0 in slots 2 and 3. Very disappointing news about the SM951, as I was waiting for it to be more commonly available with the idea of putting in a RAID 0 that was even faster than the XP941 rig in BareFeats.

XP941 in slot 2. SM951 in slot 3 and 4. If the SM951 worked properly in slot 2 then I would only be using two of those in RAID using slot 2 and 3 like Barefeats and others did.

I don't mind the triple blade RAID for now until someone works out why the SM951 isn't negotiating full speed link in slot 2. I have double redundancy back up in case anything happens.

Working with a 2009 8-Core Mac Pro 4,1 updated to 5,1 but otherwise very stock, I recorded these max sequential read/write numbers using BlackMagic (all numbers in MB/s):
XP941 alone in Slot 2 was 972.3/926.9.
SM951 alone in Slot 3 was 1427.9/1393.2.
RAID 0 with XP941 in Slot 2 and SM951 in Slot 3 was 1828.7/1514.9.
RAID 0 with XP941 in Slot 2, SM951 in Slot 3, and SM951 in Slot 4 was 1924.7/1800.0.
RAID 0 with SM951 in either Slots 2 and 3 or Slots 3 and 4 was essentially no faster than SM951 alone in Slot 3.

If anyone is going the Samsung route, I would recommend SM951 in Slot 3. If anyone is going the Samsung route and wants to RAID 0, then--although I did not test this combination as I have only one XP941 at the moment--using two XP941s might be the best solution in terms of bang for the buck. I wish I had been able to get the numbers macprouser did with the XP941/SM951 RAID 0, but there are many variables and measuring sticks and, for whatever reason, I did not come close to 2300 MB/s.

Just a note that Samsung started shipping a newer version of the SM951, with a NVMe interface instead of AHCI. Check your part numbers before buying, if it matters to you:
 
MZ-HPVxxx (AHCI)
MZ-VPVxxx (NVMe)
 
The older AHCI interface has a few advantages, most notably much wider system compatibility, at least for now. But NVMe is faster and better. IOPS's are substantially increased compared to AHCI.
 
As for RAID use of SSDs, not a smart choice imo. The constant writing required to maintain a disk array dooms these drives to short lifespans. Also, according to reviews an uncooled SM951 reaches its auto-throttle temp in under two minutes of heavy writing.

Good information, thanks. Others have reported that Classic Mac Pro seems to play nice with generic AHCI controller but not so much with SATA Express controller. When the dust settles, I may keep a single SM951 512GB, which is pretty fast and can hold everything that I do not archive. Being a nontechnical guy, though, I am curious as to why RAID 0 would take a greater toll on the drives--isn't it just writing half of a file to each drive?

GregoryOrme
Good information, thanks. Others have reported that Classic Mac Pro seems to play nice with generic AHCI controller but not so much with SATA Express controller. When the dust settles, I may keep a single SM951 512GB, which is pretty fast and can hold everything that I do not archive. Being a nontechnical guy, though, I am curious as to why RAID 0 would take a greater toll on the drives--isn't it just writing half of a file to each drive?

Not quite. I'm talking about true RAID. "RAID 0" is a misnomer, since there's absolutely nothing redundant about a RAID 0 array. So controller overhead is negligible compared to the actual RAIDs (1/5/10/etc).

Ok..I'm running into an issue with my SM951 AHCI version. For some reason when I try to open files or run programs I'm getting a 3 to 4 sec delay. I'm using it at a storage drive and my main drive is an Intel PCie 750 SSD. My motherboard is an Asus X99-E WS and I have a Core i7 5930K. Running 64GB of ram. I also have 4 WD 4TB in RAID 10 config with no delay when I use them. My Main drive also has zero delay. Any thoughts?

Ok..Problem solved...I removed/reinstalled the GPU drivers..