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Fastest Scratch? RAM, SSD, RAID 0?

S

sammyman

macrumors 6502a
Original poster
Mar 21, 2005
998
65
I have been reading around trying to figure out what would be the best scratch disk for me. I read somewhere that RAM is the fastest. I will have 32GB, will that cover me, so I won't need a different scratch disk? Then I read SSD, but that they can get worn out quickly as a scratch. Then I read that RAID 0 7200rpm drives are super fast as well.

I am hoping to either use a 640gb 7200rpm drive that came with the Mac Pro, or maybe just let it use RAM. I don't really want to buy another SSD drive since they are so pricey.

Any thoughts?
 
Ram is the fastest form of scratch disk.

Run these in Terminal to get the size you want. Making a raid disk is the only way to get more than 2.2gb of space in ram.

1.25GB
diskutil erasevolume HFS+ "RaidRamDisk" `hdiutil attach -nomount ram://2650000`

2.2GB
diskutil erasevolume HFS+ "RaidRamDisk" `hdiutil attach -nomount ram://4612000`

3.5GB
diskutil erasevolume HFS+ "r1" `hdiutil attach -nomount ram://3959731`
diskutil erasevolume HFS+ "r2" `hdiutil attach -nomount ram://3959731`
diskutil createRAID stripe RaidRamDisk HFS+ /Volumes/r1 /Volumes/r2

5.3GB
diskutil erasevolume HFS+ "r1" `hdiutil attach -nomount ram://3959731`
diskutil erasevolume HFS+ "r2" `hdiutil attach -nomount ram://3959731`
diskutil erasevolume HFS+ "r3" `hdiutil attach -nomount ram://3959731`
diskutil createRAID stripe RaidRamDisk HFS+ /Volumes/r1 /Volumes/r2 /Volumes/r3

6.2GB
diskutil erasevolume HFS+ "r1" `hdiutil attach -nomount ram://4612000`
diskutil erasevolume HFS+ "r2" `hdiutil attach -nomount ram://4612000`
diskutil erasevolume HFS+ "r3" `hdiutil attach -nomount ram://4612000`
diskutil createRAID stripe RaidRamDisk HFS+ /Volumes/r1 /Volumes/r2 /Volumes/r3

8.2GB
diskutil erasevolume HFS+ "r1" `hdiutil attach -nomount ram://4612000`
diskutil erasevolume HFS+ "r2" `hdiutil attach -nomount ram://4612000`
diskutil erasevolume HFS+ "r3" `hdiutil attach -nomount ram://4612000`
diskutil erasevolume HFS+ "r4" `hdiutil attach -nomount ram://4612000`
diskutil createRAID stripe RaidRamDisk HFS+ /Volumes/r1 /Volumes/r2 /Volumes/r3 /Volumes/r4
 
I recall reading that Ramdisks were a waste of RAM in OSX... since the OS will cache the most frequently accessed storage I/O in RAM anyway - to reduce disk activity. When using a RAMdisk, you're effectively storing two copies of that stuff in RAM... the content on the Ramdisk and a copy that OSX is maintaining in the RAM disk cache.

I would use an SSD for scratch if you can afford it, and make sure you have sufficient RAM so that most of your work is cached in RAM anyway.
 
I had also heard that A RAM disk was a waste of RAM and the bennefits not great. Seems an internal and dedicated SSD is the best.
 
TechnoDestructo said:
Application ram and scratch data are not even close to the same thing.
Click to expand...

What part of my comment did you think said it was? You can allocate system hardware RAM as a RAM Disk. We used it alot in early versions of photoshop 3, 4 etc because disk speed was so slow. But the bennefits of using one in this day and age aren't as great and you are just wasting RAM when the app can utilise it.

OP, I have 32GB of RAM also and it really takes care of the most heavy tasks (ie 10+GB PSB files in photoshop). I have a 4 Disk 7200 Raid 0 that in some ways is faster than my 2x Raid 0 SSD. In other ways the SSD is much faster. Scratch works well with SSD's as there is more time wasted in mechanical components latency and finding small pieces of info. So my Mechanical RAID lets its self down random and my SSD's shine in this.
 
Last edited:
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