SSD RAID 0

Question

Hello,
I recently purchased two Intel X-25M 160GB SSDs. I put them in RAID 0 via Disk Utility. However, I was wondering what the best block size would be for my boot drives. I currently have it in 128k blocks, and it is very slow compared to my MacBook with one SSD and no RAID. Is there any way to improve the performance? Would it be better to just use one SSD in the Mac Pro? Would setting the block size to a different setting improve the boot volume?
Thanks!

Answer 1

Congrats on entering the world of SSD!!! You should keep in mind that not all SSD are created equally. Intel SSD are usually a little slower than some other brands but have a longer lifespan. SSD technology suffers from a limited amount of writes to each cell before the cell fails. If your MacBook SSD is SandForce based you will likely see better performance than the two Intel units, even in a stripe.
When purchasing an SSD do the research on who makes the controller, this is the most important aspect of current SSD based drives. The list of will include Intel, Toshiba (think MBA, Kingston ssdNow series), Indilinx (OCZ Agility), SandForce (OCZ Agility 2, OCZ Vertex 2, OCZ RevoDrive, Corsair F Series, OWC Mercury series), Marvell (Micron/Crucial C300)
As for the block sizes, I would pick a smaller size than 128k for SSD as they really shine in small random access workloads.
I boot my MacPro (1,1 , 2.66ghz) from a Kingston 64 gig SSD. This model is a Toshiba based unit. It performs nicely as a boot device.
I have 2 x 1 TB Western Digital Caviar Black drives in a stripe to hold video and "slower need" data.
I have 2 x 240 GB OCZ RevoDrive (first model, not the updated X2 series) to hold Aperture Libraries. These drives have an onboard stripe which I disabled on a PC during post. Each RevoDrive exposes 2 x 120 GB drives to OS X. I take the "4" drives and stripe them in disk utility using 32K Raid Block Size.
I have a 2 TB Western Digital Caviar Green for Time Machine
I use diglloyd DiskTester for benchmarking. Please note that if you get this tool DO NOT use his Recondition SSD feature as it is only useful on early SSD technology. It slowed my Crucial C300 to the point where I had to re-flash the firmware (which does a low level format)
Results are from Sequential Test command in DiskTester
*Kingston -- (Avg / Fastest / Slowest) -- MB / Sec*
Write - 158 / 176 / 149
Read - 238 / 242 / 232
*WD Caviar Black Stripe*
Write - 186 / 191 / 175
Read - 191 / 202 / 166
*OCZ RevoDrive (Stripe of 4 SandForce based "drives", 2 from each RevoDrive, 32K Block)*
Write - 704 / 717 / 699
Read - 936 / 958 / 865
*OCZ RevoDrive (Stripe of 4 SandForce based "drives", 2 from each RevoDrive, 16K Block)*
Write - 689 / 701 / 655
Read - 943 / 950 / 920
*OCZ RevoDrive (Stripe of 4 SandForce based "drives", 2 from each RevoDrive, 256K Block)*
Write - 696 / 702 / 685
Read - 904 / 916 / 882
*OCZ RevoDrive Single Drive* +(I copied my data off the "Stripe" and tested a single drive, this should be on par with what you can expect from a single SandForce based unit such as a Cosair F series, OCZ Vertex 2, etc)+
Write - 221 / 223 / 217
Read - 266 / 268 / 260
For Comparison I will also post results from my MacBookPro (6,1 , i7 2.66)
*This drive is a Crucial C300*, 256 GB, boot. This drive has been installed for about 5 or 6 months.
Write - 213 / 223 / 209
Read - 280 / 281 / 278
I hope this gives you a better idea of various SSD technologies. As you can see there a great variation in speed when you compare the Kingston (toshiba based controller) to the Crucial (Marvell based controller). The C300 is on par with the Single SandForce Based Unit.
I will add that I have 2 more SSD in non Mac systems. A Corsair F60 and F120. Both are in Dell Laptops and they perform on par with the single SandForce results from above. Also note that the C300 is a Sata3 (6 Gbit) drive that is running on Sata2 (3Gbit) connection. Most online reviews claim that the drive performs better on the higher speed bus, but I cannot confirm.