How much cache does a typical desktop really need?

[deimos3428]

The idea of using a small (20-40GB) SSD in front of a magnetic disk for file caching is getting a lot of attention lately. That'll run about $100 or so.

But for about $150, you can get 16GB of DDR3. Most systems are only going to use about 4-6GB as RAM; the rest will be available for file cache. Of course, RAM is much faster.

So the question becomes, how much cache does a typical desktop really need? Would 6-10 GB be sufficient, or are the larger sizes made possible by SSDs actually useful to most people?

 

[Emulex]

who are you talking about?
I need two 30" displays so 16GB of ram is very welcome. ssd is nice but i'm not doing any streaming - just coding/office/bunch of putty/tons of browsers.

I'd just prefer to have a ssd drive and backup plan and that is all. nothing fancy.

 

[groberts101]

"typical" is far too broad a term to use any more. Some "typical users never shut anything down and just keep opening more and more apps and browser tabs. Some close things and move on so it would be very user specific.

SSD size is more about write stamina and most don't understand that thinking that when they buy more capacity?.. they get to use it all. Is bad for write endurance and increases degradation/recovery times.

Is like buying a car with 300 Horsepower. No one says you must use it all and is just there if you need it.

 

[deimos3428]

Let me try another tack.

I'm assuming a motherboard capable of at least 16GB in this scenario, and working under the assumption that it will never be fully utilized. While I'll concede some users are the exception, the vast majority of home/office PCs do not consume that much and likely never will.

So given the above, is there be any advantage *beyond cache size* to using an SSD over filling all available RAM slots?

 

[Cerb]

The idea of using a small (20-40GB) SSD in front of a magnetic disk for file caching is getting a lot of attention lately. That'll run about $100 or so.

But for about $150, you can get 16GB of DDR3. Most systems are only going to use about 4-6GB as RAM; the rest will be available for file cache. Of course, RAM is much faster.

So the question becomes, how much cache does a typical desktop really need? Would 6-10 GB be sufficient, or are the larger sizes made possible by SSDs actually useful to most people?

They are not applicable to each other. Such an SSD cache would hold data between reboots, and allow burst writes to the HDD, during otherwise low-activity times. An ideal SSD cache would also keep search indices and smaller files in it, to reduce waits due to repeated seek latencies on the HDD, and selectively buffer writes, based on learned usage pattaerns. In this scenario, how do you replace the larger SSD with smaller RAM? The problem here is that you want to keep the worst-performing parts of your filesystem access from allowing the HDD to be a bottleneck. Having more space to do it in, and being able to rely on that cache being persistent between logins and reboots, will facilitate that far better than a little bit of fast RAM.

That RAM cache has to repopulate every power cycle (and, do you want it to be persistent, such that it writes that out, and reads it back, delaying your shutdown and startup times?), and its utilization will vary by day, and by user, just like 'utilized' RAM will. I have 8GB, FI, and neither Windows nor Linux will use all of it for caching. I typically have 1-2GB completely free (since I don't run RAM-hungry games in Linux, it's sometimes 3+GB). Some people, OTOH, have 12-16GB, and can get it all used for caching. It all depends.

 

[Denithor]

deimos, are you talking about creating a ramdisk with the remaining 10GB? And then 'caching' your frequently used programs there? Or just having 16GB of RAM available in the system resources?

 

[deimos3428]

deimos, are you talking about creating a ramdisk with the remaining 10GB? And then 'caching' your frequently used programs there? Or just having 16GB of RAM available in the system resources?

Nope, I was talking about regular file caching by the OS. I have 16GB, but sadly I've never made use of more than about 8GB, including file cache. So I have to question the utility of an even greater amount of relatively slow cache in that scenario. People who can use more cache than they have RAM would benefit considerably of course. Cerb made a great point about the persistency of the cache across reboots, still wondering if there are any further benefits.

 

[ElenaP]

Buffered writes in RAM are not delayed for long, because of the risk of loss of power or hard crash. Buffered writes on SSD can be delayed as long as there is a free space on SSD.