Ram disk

Is there an speed improvement in using a ram disk ?

http://askubuntu.com/questions/15286...ake-a-ram-disk

Created my ram disk and pointed my browser cache to it.

sudo mkdir -p /media/ramdisk sudo mount -t tmpfs -o size=2048M tmpfs /media/ramdisk

free -m shows this. Where is the ram disk ?

total used free shared buff/cache available Mem: 6.8G 679M 4.8G 35M 1.3G 5.7G Swap: 0B 0B 0B

obviously a ram disk is going to be faster than a mechanical drive, but whatever you use in the ram dksk is not available to programs so may cause more use of swap, also if you need to save the data after power down you will need to write it out to a 'real' disk all of which takes time, it's swi ngs and roundabouts really

p.s. I beleive the ram disk will frow as needed so a fresh ramdisk will not use much memory untill u start writing to it

Originally Posted by Keith Hedger obviously a ram disk is going to be faster than a mechanical drive, but whatever you use in the ram dksk is not available to programs so may cause more use of swap, also if you need to save the data after power down you will need to write it out to a 'real' disk all of which takes time, it's swi ngs and roundabouts really

I am aware of that.

A browser cache never needs to be saved.

I have 8 Gb of ram, of which only 2 Gb is ever used.

A ram disk is even faster than a SSD drive.

When burning CD/DVDs I notice that CPU usage is very high, but I think the burner program uses RAM for it's cache.

tmpfs is incredibly fast. I even blogged a how-to on customizing boot scripts to load the entire OS into a tmpfs ramdisk. It's faster than any SSD. And it honestly does NOT slow down a system if you have swap. tmpfs can be offloaded into swap space, which reduces the performance of any files offloaded down to the level of normal files on a normal partition...but this is not really worse than the performance had those files been on a normal partition in the first place.

The differences in performance are more subtle. Basically, a normal file on a normal partition will receive writes at some point when the drive is free to accept the updates. In all cases, writes first go to the RAM cached file. If it's backed by a normal partition, then this update will be written to disk eagerly...as early as convenient. After being written to disk, the cached portion is marked as clean (so it can be flushed from RAM at any instant to make way for something else needing RAM).

tmpfs is basically just a RAM cache with no disk file system backing it. As such, there's nothing to write updates to. Its files can never be marked clean. But they can be offloaded into swap...not eagerly, though. It'll only get offloaded at the last second, when the RAM is needed. This may cause a noticeable speed bump as whatever needs the RAM waits for it. So maybe you'll notice some slower performance. Maybe. But once it is offloaded into swap, that RAM is now available. As long as the offloaded files aren't accessed again, it just sits on swap not impairing performance at all. Just like any normal file just sitting on disk.

Now, there's the question - "Where is it?" when you look at the output of "free". Unfortunately, the data returned by "free" does not account for tmpfs in a neat way. The problem is that tmpfs is implemented as a file cache that just happens to not have a normal file system backing it. As such, it's included in with "cache". But everything else in "cache" is not really used up in a way that makes the RAM unavailable. Normally, "cache" is nothing but blocks that are either clean or will be clean soon enough. Any clean blocks can be dumped from RAM in a flash.

But tmpfs breaks that assumption. Any tmpfs cache will NEVER be clean. They will ALWAYS be dirty, because there just isn't any backing file system.

Interesting.

Thanks for the explanation.