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.

Thanks. That makes sense, and that is one quick rig.

GregoryOrme
Although I remain curious because I thought the rule of thumb for RAID 0 is that the configuration would be limited by the slowest drive (XP941), which makes me wonder if the performance gain from the two XP941 setup to the one XP941/two SM951s setup could be attributable to striping across three drives rather than two. That is, would you have seen the same performance with three XP941s as with the one XP941 and two SM951s?

The PCIE slots 3 and 4 share the same bandwidth in the Mac Pro due to some limitation of the X58 chipset so no, three XP941s would be no faster. About the same.
 

GregoryOrme
My only concern with the XP941 RAID 0 configuration is that my Mac Pro is running Yosemite and it apparently does not allow third-party TRIM enablers to work. I am concerned about degradation of performance over time in the RAID.

Yeah but by the time the SSD even degrades 20% it will be time for another upgrade anyway. But if you want to hang on to the same SSD for a long time then get the Apple versions of the XP941 or SM951. They have different model serial numbers and you can get them on eBay if you look closely at the photos. Search 'Apple Samsung SSD'. If the photo shows SSUAX that is XP941. If it shows SSUBX that is SM951. These are TRIM compatible without any third party hacks.

Just remember SM951 / SSUBX are not working at full speed in slot 2. So maybe they are not worth it right now and stick with XP941 / SSUAX.

GregoryOrme
Truth!

Someone has uploaded a video on YouTube with three SM951 striped in RAID with about the same score as me. I can't paste video here as that is disabled. You have to search 'sm951 mac pro'

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.

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.

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?

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?