SSD/HD hybrids are little used

C

Carlo Milanesi

New Member
Since four years ago, SSD/HD hybrid storage units look to me (I am a software developer, not an hardware expert) a great idea to improve the performance/cost ratio of computers, and therefore I expected they become as ubiquitous as CPU caches. Instead, I see such hybrid storage systems are quite rare, and only of high-end computers. Why?

Keeping into account current prices of 8 GiB Flash memories and their supporting controllers, I would expect the additional price of such hybrid systems would be no more than $20 for 8 GiB caches. Instead they are much more expensive. Why?

Speaking of performance, everyone says that such systems speed up read access for frequently used files, but they do not speed up write access.
But I think the caching system could store on an SSD data written during intensive processing, and then, when the computer is underutilized, to copy such data to the magnetic device. Why it is not done?

I see all SSD caches are of 8 GiB. Such size is good read caches. Though, if an SSD cache is to be used also for temporarily saving writes, for some usage patterns, like video editing, it not enough, because such application write burst of more than 8 GiB of data. Why there aren't SSD caches of 16 or 32 GiB, that would be inexpensive anyway?

Thank you.

--
Carlo Milanesi
 
The cost of SSDs have dropped dramatically, so getting 256GB or 512GB of 100% flash isn't that outrageous anymore.
 
Keep in mind too that the OS already caches with free RAM space.

But I think the caching system could store on an SSD data written during intensive processing, and then, when the computer is underutilized, to copy such data to the magnetic device. Why it is not done?
Click to expand...

That would be difficult when the size of the data exceeds the size of the cache. Also, if you stored your writes into cache it would purge what you have cached from reads so you'd be back on the mechanical portion to pull other data you'd want to read.
 
Okedokey said:
Because the ssd cache used is often too small, negating any performance improvement.
Click to expand...

Geoff said:
The cost of SSDs have dropped dramatically, so getting 256GB or 512GB of 100% flash isn't that outrageous anymore.
Click to expand...

These two combined is why. If you wanted to create a bigger cache the price increase would almost be as worthwhile as just getting a pure SSD, as is the case with many people these days. My 120GB 840 Evo has had it's price almost cut in half since I got mine a little over a year ago. I could get a drive over twice the size for about what I paid last year.
 
I am not convinced by answers.
A read SSD cache as large as the installed RAM *is* enough to keep all program and configuration files that are loaded into RAM. Otherwise RAM has to be overwritten.
This speed-up start up time of operating system and of application software.
And a write SSD cache is enough if it has a size larger than that of all the files used in a session (say, a couple of hours). Of course, the size of all the files used in a session varies hugely according the application. For example, for work processing or spreadsheet, typically few megabytes of data are used in a session, while for video editing many gigabytes of data is used in a single session.
I know that the operating system has a disk caching system, but until data is saved on a persistent support, a save operation (or database commit) cannot be completed.
The cost of SSDs has dropped, but most desktop and notebook computers still have only magnetic storage.

--
Carlo Milanesi
 
Carlo Milanesi said:
The cost of SSDs has dropped, but most desktop and notebook computers still have only magnetic storage.
Click to expand...

That's because manufacturers are still too cheap to put out cheap new machines with SSD's because the price point is still higher per GB than traditional mechanical drives. Consumers like cheap, and companies cut as many corners as they can to put out the cheapest machine they can.

Believe me, I know people like cheap. I sold PC's for years.
 
You must log in or register to reply here.
Back
Top