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FuNGi
Sep 5, 2012, 07:53 AM
A friend has been wondering if having less RAM with a SSD is less of an issue than with a HDD because the swap will take place much more quickly. Any thoughts?



simsaladimbamba
Sep 5, 2012, 07:59 AM
Current notebook HDDs have sequential read and write speeds of about 70 to 90 MB/s.
Current SSDs have sequential read and write speeds of about 250 to 600 MB/s, mostly averaging at around 450 MB/s.
Current DDR3 RAM have sequential read and write speeds of about 6,000 MB/s to 17,0000 MB/s.
Having an SSD while having less RAM can help make the paging out faster (copying content from RAM to SSD or HDD), since SSDs are faster than HDDs.

If your reasoning is because of budget issues, also know, that an MBA SSD can be upgraded via www.macsales.com and the Aura Pro product.

FuNGi
Sep 5, 2012, 11:11 AM
Thanks for the info. THat's quite a speed difference!

KPOM
Sep 5, 2012, 11:30 AM
It is somewhat less noticeable since the SSDs are fast (the 2012s get read and write speeds in the 400-500MB/s range), but if you are running something memory intensive such as a virtual machine, more RAM still helps.

plucky duck
Sep 5, 2012, 12:16 PM
With only 4gb of ram I've managed 1gb of page outs on an ssd with multiple browser tabs (10), apps, and final cut rendering a clip, all things considered it was a positive surprise how well OSX still responded to user inputs and UI was still very smooth. SSD does not chew up CPU cycles like a HD does when under full load.

dyn
Sep 5, 2012, 12:30 PM
Current notebook HDDs have sequential read and write speeds of about 70 to 90 MB/s.
Current SSDs have sequential read and write speeds of about 250 to 600 MB/s, mostly averaging at around 450 MB/s.
Current DDR3 RAM have sequential read and write speeds of about 6,000 MB/s to 17,0000 MB/s.
Having an SSD while having less RAM can help make the paging out faster (copying content from RAM to SSD or HDD), since SSDs are faster than HDDs.

If we are talking fileservers, databaseservers, etc. that actually move around large amounts of data that are also quite big than yes.

But we are not talking about any kind of server, we are talking about a small ultrathin notebook from Apple in which case sequential speed doesn't matter at all. These kind of speeds are solely marketing terms for these kind of systems. The only reason why having less RAM isn't that big of a deal on something like the Air is because of the other characteristics of the ssd: very very low latency, very high read/write speeds for very small data (the so called random read/write speeds) and a very high amount of iops. These 3 things are also the main reasons why virtualisation works so well on these little notebooks.

So yes indeed, an ssd is faster than a hdd which helps tremendously when swapping but it isn't because of the sequential read/write speeds, it's because of the other things (latency, iops, random read/write speeds). However there is a limit to this. An ssd helps a little, having the right amount of memory and using the proper settings (when using a vm, in Photoshop, etc.) helps a lot more. One should not see an ssd as the solution to not having enough memory.


If your reasoning is because of budget issues, also know, that an MBA SSD can be upgraded via www.macsales.com and the Aura Pro product.
That depends on your data: if you have lots of uncompressable data (when you use something like Filevault 2 you'll have this) then the Apple ssd is a better idea since it is faster than the OWC one. The OWC Aura Pro uses a Sandforce controller which works the best when using compressable data and performs very worse with uncompressable data. It also consumes more power than the Apple ssd which could mean about half an hour less battery life. On the other side: the OWC Aura Pro is still very fast and you'll still have enough battery life but you gain lots of storage space. Alternatively you could use an external drive which is a lot cheaper (with the 2012 MBA model you can even use usb3 and still have high performance).

robvas
Sep 5, 2012, 12:50 PM
I have a 2GB Air - I can definately tell when it's paging. It's nowhere near as bad as a 5400RPM hard drive, but it's very noticeable.

You're probably looking at a 100x speed difference between RAM/SSD.

plucky duck
Sep 5, 2012, 02:40 PM
I have a 2GB Air - I can definately tell when it's paging. It's nowhere near as bad as a 5400RPM hard drive, but it's very noticeable.

You're probably looking at a 100x speed difference between RAM/SSD.

For what application or tasks do you notice the paging? Does the system become unresponsive? Delays in user input?

robvas
Sep 5, 2012, 04:23 PM
For what application or tasks do you notice the paging? Does the system become unresponsive? Delays in user input?

3 browsers open, lots of tabs, Xcode, 2 text editors, handful of terminal windows. Nothing crazy but I get into 1GB of pagefile use. It's just a stutter or delay - it'd be unusable if I had a regular HD but having 4GB would be nice.