120GB Mercury extreme Pro 6G SSD

[AFX]

Hey Guys,

Today I received a pair of 120GB Mercury extreme Pro 6G SSD drives which I was planing to setup in RAID 0 in my 4,1 MacPro however one of the drives fails to show up in Disk Utility.

After spending the day trying to get it to work I decided to just install on the one SSD which I was amazed at the performace gain. I was planing to send the faulty drive back for a replacement and use the one drive utill the new one arrives when I came across this:

If you are planning to boot from a RAID 0 array, you may not see any better performance than you would booting from a single SSD. That's because the RAID set can't do any more transactions per second than a single SSD. And the random small transfer rates are only slightly higher with two versus one. And three or four were no faster than two. The main reason for booting from a multiple 6Gb/s SSD RAID set would be for the extra storage capacity. You might consider booting from one 6Gb/s SSD and using a striped set of three or four to use as a scratch volume or working capture/playback volume.

Source

I know I'm not using a host adapter and that my system is not capable of taking advantage of the full 6Gb/s so its not a direct comparison but does this mean theres no extra performance from a second drive?

I'm just trying to work out if I should get a refund or a replacement for the faulty drive.

Cheers.

 

[philipma1957]

the answer is multi part.


mac pro is sata II the max speed 1 ssd can do for a clone or sustained file transfer is 250 to 280MB/s. so if you had 75 gb of info on the drive and used super duper to clone it top clone speed would be 250 to 280 mb/s if you were cloning it to another ssd.

now if you had 2 120 gb ssd's in a raid0 and a second set of ssd's in a raid0. they both could read and write large files close to 500mb/s. so if you cloned the first raid to the second raid it would be fast maybe 500Mb/s. now you hardly ever clone the osx maybe 1 time a week at night if you have a scheduled backup. so the speed would almost never been seen. so in the one case that your get real easy to see speed increase you don't get to use it much at all.



now for the second part. your iops for osx don't go at 250MB/s or if you are raid0 500MB/s they are slower maybe 50 MB/s (a hdd is 1MB/s) these will gain a bit. But at a price the raid0 is more then twice as likely to fail then a non raid 1 ssd. also 1 ssd your gain was 1MB/s to 50MB/s a raid0 ssd your gain may be 50MB/s to 75MB/s so it is not a big gain like hdd to ssd is and failure rate will go up..


This set of answers are simplified and reduced quite a bit. Having used a lot of ssds I always say get the biggest one you can afford and make backups. I have found that for osx and permanent files one ssd is more stable then a raid0.

 

[VirtualRain]

Striped SSDs improve sequential read/write speeds. In fact, internally all SSD's are effectively RAID0 arrays of NAND chips for this reason. However, a lot of desktop I/O is random small transfers which doesn't benefit.

So SSDs in RAID0 certainly doesn't hurt and it might make a difference in reading large photos libraries or in video work, but I wouldn't go out of my way to go this route if you're starting from scratch.

It may make sense if two smaller drives are cheaper than a single larger one, or if you are adding a second drive to increase capacity to one you already have.

Things you give up with RAID0:
- An extra drive bay
- Added risk of data loss due to drive failure
- TRIM does not work on RAID arrays
- Potential lack of portability of your data between different systems

 

[AFX]

Thanks for the replies. Given the price vs gain of the extra SSD I think I'll just get a refund and get some more memory instead.

Thanks for your help!