On Tue, 01 May 2012 09:04:01 -0400, Paul wrote:

wrote:
What's the difference between:

installing your OS and all your programs on the SSD

and:

using the SSD as a cache drive?

If both options give you equal performance in terms of speed what
would be the advantage of going with the cache drive option?

Jon

When you have the facilities to run an SSD as a cache, it "remembers"
a fraction of a larger hard drive.

Say, for example, you have a 20GB SSD and a 1TB hard drive. The
ratio between those two, is fifty to one. The SSD then, can only
"remember" 2% of the entire hard drive. And speed up, 2% of the
accesses. (This would be a read-cache.)

If the caching is intelligent, or, if you make reference to mostly
OS files on a given day, perhaps the SSD used as a cache, will end
up holding mainly OS files. And then, on the next boot, assuming
the cache concept works during the boot phase, the boot will be faster.

*******

Now, say instead, you did not use the cache concept. You used the
20GB drive as C: instead, and installed the OS. Now, any file put
on the 20GB drive is fast. But if you had any "irrelevant" files
on there, they're "wasting" storage space on your fast device.

So in balance, the cache concept allows the most recently used
things to be cached. And if the cache software is intelligent,
maybe most of what is cached is OS files, and OS related things
go faster. But if you compared benchmark performance, the
cache can never be exactly as fast as using the 20GB drive directly
as C:.

But if you used a 20GB drive as C:, you'd rapidly run out of space.
My Windows 7 laptop, uses at least 26GB as of SP1, so I couldn't
even fit all of Windows 7 on there. In which case, I might have no
option but to use some caching scheme. (Or, just install to the
1TB, and forget about the SSD entirely...)

Using a drive as a cache, in terms of the "wear" properties,
really depends on what the LRU (least recently used) policy is
doing. Say the cache is "dumb", you view a 9GB movie for a couple
hours, and in the process, the cache copies the movie to the SSD.
Now, 9GB of other files, are purged to make way for the movie.
Next, say you reboot. On the reboot, none of the tiny OS files
are on the SSD, because the 9GB of flushing removed them. So the
next boot seems slow by comparison. Until the movie is flushed from
the cache, and replaced by OS files. So as to how well the scheme
works, you need to know a lot about the caching principle, whether
all files are treated generically, or whether OS files take
priority somehow.

The idea has pros & cons, and the devil is in the detail.

Paul


Do you know if the software allows you to manually select which
programs you want to remain in the cache? In other words say "don't
allow these programs to be purged from the cache". I haven't seen a
feature like this mentioned while reading about SSD drives. That would
seem to be the solution for the 9 GB movie scenario you described.

thanks to all who answered

Jon