I have just upgraded my mac mini (late 2012) with dual Samsung 850 Pro SSD's and put them in RAID 0 mode. The weird thing is, benchmarks show read speeds of 88 MB/sec ? This is way to slow, was expecting at least 500 MB/s and over!
Any idea on what I can do here?
In Profiler
OS X: About System Information and System Profiler - Apple Support
under SATA what negotiated link speed is listed?
How are you measuring speed?
The Black Magic app?
Yes I tested with the blackmagic tool, but also with several terminal commands such as
tjeerdkramer@quarterpounder:~$ write=$(dd if=/dev/zero bs=2048k of=tstfile count=1024 2>&1 | grep sec | awk '{print $1 / 1024 / 1024 / $5, "MB/sec" }')
tjeerdkramer@quarterpounder:~$ echo $write
151.151 MB/sec
151 is actually one of the best scores I have seen. Ranges between 60 and 150 MB/s
Intel 7 Series Chipset:
Vendor: Intel
Product: 7 Series Chipset
Link Speed: 6 Gigabit
Negotiated Link Speed: 6 Gigabit
Physical Interconnect: SATA
Description: AHCI Version 1.30 Supported
Samsung SSD 850 PRO 512GB:
Capacity: 512,11 GB (512.110.190.592 bytes)
Model: Samsung SSD 850 PRO 512GB
Revision: EXM02B6Q
Serial Number: S250NXAG901360J
Native Command Queuing: Yes
Queue Depth: 32
Removable Media: No
Detachable Drive: No
BSD Name: disk0
Medium Type: Solid State
TRIM Support: No
Bay Name: Lower
Partition Map Type: GPT (GUID Partition Table)
S.M.A.R.T. status: Verified
Volumes:
EFI:
Capacity: 209,7 MB (209.715.200 bytes)
BSD Name: disk0s1
Content: EFI
Volume UUID: 0E239BC6-F960-3107-89CF-1C97F78BB46B
disk0s2:
Capacity: 511,77 GB (511.766.216.704 bytes)
BSD Name: disk0s2
Content: Apple_RAID
Boot OS X:
Capacity: 134,2 MB (134.217.728 bytes)
BSD Name: disk0s3
Content: Apple_Boot
Volume UUID: 71462A61-72B7-3BAC-91D0-93A34E417C0C
Do y have the latest firmware for the SSDs?
Do you have TRIM enabled?
I have heard of problems with the 850 Pro in Macs
http://www.mac-help.com/threads/samsung-850-evo-ssd-performance-issues.220356/
He doesn't have TRIM enabled (see his post above).
TRIM Support: No
I am only seeing details in your post for a single drive which is a Samsung SSD 850. I am sure it is not the case but if the other drive was a slow spinning metal hard drive it would slow the entire RAID down.
I don't recall it occurring on Mac minis but there have been cases of MacBook Pros fitted with two hard drives of one being incorrectly limited to SATAII instead of SATAIII, hence the need to check details of both.
Hope these screenshots help?
Thanks yes those confirm both drives are running at SATA III i.e. 6Gbps.
It maybe you have them setup as RAID1 a mirror rather than RAID0 a stripped array. With RAID0 it should give you the equivalent of a 1TB drive by 'striping' the two 512GB drives together and reading/writing half from each simultaneously. As the RAID volume is only 511GB it looks like you have a RAID1 array whereby an exact duplicate copy is on both drives. This means that if a single drive fails you still have all your data but it also means it has to write a copy to both drives which of course takes twice as long. I would however not have expected it to cause a slow down in reads as it only needs to read one copy.
Here is a very rough diagram to illustrate how RAID0 and RAID1 would differ.
(-512GB-)
Drive A = AAAAAAAA
Drive B = BBBBBBBB
(-512GB-)
RAID1 = 11111111
11111111 i.e. both drives have same content
(-----1TB------)
RAID0 = 1212121212121212 i.e. each drive has half the contentThere is also the issue that software based RAID like you are using is always slower than a hardware based RAID, and Apple's particular software RAID is also slower than for example SoftRAID5. See http://www.softraid.com
Even so your read speeds are far slower than I would expect.
If it is possible I would consider wiping it all and setting it up again from scratch.
I have removed the RAID altogether, erased the drives, and tested again. Still very poor performance (write 80-120 MB/S, read max 200 MB/s). Both drives seem to have the same kind of performance...
Try the following:
Run the trimforce command. Upgrade your Machine t o at least 10.10.5 or 10.11. Now run the following command from the Terminal:
"sudo trimforce enable". Enter in your password.
Hit enter. Read the scary Apple warning message and say Yes. Say yes to rebooting the machine.
This will make a big difference.
You are running a SATA 6/GB /sec capable Intel chipset, so you definitely should be hitting over 500 Megabytes per second.
Slow performance with Samsung 850 pro SSD in raid 0