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View Full Version : Suggestion: Flash memory as HD cache?


mcs37
Mar 25, 2003, 11:35 AM
Hey everyone. I had an idea the other day and wanted to float it. Why doesn't a company like Apple use flash memory to act as a hard drive memory cache?

Imagine this: you have your 60 GB drive in your 17" Powerbook. But this is Rev B using Panther, and Apple has installed an additional hardware component in your box: 512 MB of flash memory. Now why in the hell would anyone want flash memory in a laptop with 60 GB? Simple: powersleep. I don't own a powerbook but I plan to buy the 17" PB rev b (I hear it might have 1.25 GHz G4). I've seen the Apple powerbooks and I love them, and I've noticed their sleep feature is really nice. Why can't we extend that more? Make the first laptop that truly powers on in seconds. We can't accomplish this with hard drives well since it's slow to come out of hibernation. And we can't use RAM since it's volatile. Only in the past couple of years have we seen a significant growth in flash memory capabilities. Nowadays you can get even a GB of flash memory for several hundred dollars, but the prices continue to fall.

Some day we'll have 100 GB flash memory cards as the standard (hopefully) so this idea will be obsolete, but until then: when you close your laptop and it sleeps, it stores all programs (user processes and the kernel) into Flash memory to preserve the snapshot. Then it shuts down, cuts power entirely. When you bring it back to life hours, days, years later, it loads everything into memory from the memory cache.

This also could be applied as a handy cache for secondary memory. Hard drives only come with 8 MB of cache usually, so using flash memory storage we could build a virtual cache on top of the hard drive. Your web server would cache most popular pages, MySQL would store a chunk of indices into flash as a backup to primary memory cache, and essentially OS X would use your 512 MB as a nice chunk of memory to hold non-volatile media.

I think there is a good potential here, and I'd be very hip to using a laptop that could boot only once every few months and powersleep in between kernel reboots. Hell, using the flash virtual HD cache you could reboot instantly as well. The hard drive essentially becomes a backup storage facility for your divx movies, images, and video files.

What do you think? Are they already using this in the powerbooks or is this is any way an original idea? I'm open to all comments. Remember I'm ignorant as to how sleep works in a powerbook. I'm only an aspiring switcher (when I can afford it in a month or two). :)

Cheers,

Mike

crapple33
Mar 25, 2003, 12:27 PM
Yes! This is a great idea! For awhile I've thought about how great it would be if we could have completely flash hard drives. Everything would be sooo fast. But since right now we're not at that capacity yet, this would be a great way to start. The largest flash card I know of right now is 1 gb, but at the rate things are going... Who knows?

szark
Mar 25, 2003, 12:43 PM
Actually, they do have complete flash memory drives for the server market, but they are VERY expensive right now.

If only I could remember where that link is...:confused:

vniow
Mar 25, 2003, 01:23 PM
I remember reading somewhere on some PC site where this was actually done, I'll see if I can find the link.

Also remember some company selling 5GB or so flash drives that hooked directly to the PCI slot, they were big and expensive, but damn speedy.

mcs37
Mar 25, 2003, 01:26 PM
Originally posted by vniow
I remember reading somewhere on some PC site where this was actually done, I'll see if I can find the link.

Also remember some company selling 5GB or so flash drives that hooked directly to the PCI slot, they were big and expensive, but damn speedy.

Imagine hard drive seek times measured in nanoseconds! But you see the idea I have here of the cache. Since we don't have cheap 200 GB flash cards yet, you don't have to store those 700 MB divx movies in cache, those go into long-term old-school spinning-disk storage. And for $220 for a 1 GB compactflash card, by the time a system with this came out (6 months from now at earliest?) the prices would hopefully have dropped more. Just imagine how great it would be if most of the work you did was BLAZING fast, plus the powerbook could sleep for years without draining any power at all. The new powerbooks would drain your entire battery after 16 hours or so while sleeping. This could be the first true instant laptop. I think it's worth looking into, Apple.

timbloom
Mar 25, 2003, 01:34 PM
This would be cool, but the cost would be outrageous, and many of us have a gig or more of RAM.

mcs37
Mar 25, 2003, 01:37 PM
Originally posted by timbloom
This would be cool, but the cost would be outrageous, and many of us have a gig or more of RAM.

What do you mean by outrageous? I'd pay an extra $200 for a laptop that slept for months without draining power, came back from sleep in under 3 seconds, could reboot entirely in under 15 seconds, and could be insanely fast using the built-in flash cache. It's too cool! I think I should e-mail this idea to Apple, I think it really has potential.

By the time anything would be implemented that cost would be maybe $150 extra. But those features could be implemented using the "flash cache." Think about it. Rebooting in 15 seconds! Less power consumption from hard drive. Incredibly fast seek times.

Cheers,

Mike

timbloom
Mar 25, 2003, 01:49 PM
Originally posted by mcs37
What do you mean by outrageous? I'd pay an extra $200 for a laptop that slept for months without draining power, came back from sleep in under 3 seconds, could reboot entirely in under 15 seconds, and could be insanely fast using the built-in flash cache. It's too cool! I think I should e-mail this idea to Apple, I think it really has potential.

By the time anything would be implemented that cost would be maybe $150 extra. But those features could be implemented using the "flash cache." Think about it. Rebooting in 15 seconds! Less power consumption from hard drive. Incredibly fast seek times.

Cheers,

Mike

It is a great idea, and I would be up to get it too. But you would need at least as much as the Max RAM which is 1 gig on the current powerbook, probably more in the future.

Also, would flash memory produce a real speed difference? My ibook wakes up within a couple seconds anyways, since the ram is still active.

mcs37
Mar 25, 2003, 01:56 PM
Originally posted by timbloom
It is a great idea, and I would be up to get it too. But you would need at least as much as the Max RAM which is 1 gig on the current powerbook, probably more in the future.

Also, would flash memory produce a real speed difference? My ibook wakes up within a couple seconds anyways, since the ram is still active.

Would you really need to store max RAM though? OS X could arbitrarily store some components in secondary storage if it couldn't fit the most popular components in primary memory. So the kernel, for instance, is stored in the 1 GB cache, while, say, your divx file's memory instructions are written to some place in /tmp. Sure it would take a second or two for them to come back to life, but the OS itself would be back and alive.

As for flash producing a difference, what I hear is that in OS X the sleep doesn't work as well as it does in OS 9 powerbooks. I hear OS 9 powerbooks can sleep for months without draining power, while the OS X powerbooks drain power quickly (over x < 24 hours). You mention the RAM is still active--using a non-volatile chip, the RAM wouldn't have to be active until it was powered on again. Saving more juice.

But remember the primary idea behind using the 1 GB is not the hibernation advantages. It lies in the HD cache, which could really prove to be valuable, I think. Caches in CPU's have proven to show their potency, especially in servers. HD caches should be just as rewarding. And 1 GB would be great. But don't forget super-fast reboots (bootup code placed into the cache, as are components called in that code). Finally, I'm sure flash cards require much less power than a HD, so you could save power even more by using the cache exclusively when you're unplugged. So popular items like Safari and your documents are all stored on the cache, saving more juice when the HD sleeps.

Mike

vniow
Mar 25, 2003, 02:19 PM
Check out this link, seems like someone did it on an older Powerbook.

http://www.pbsource.com/contributions/readers/FlashRAM_and_PowerBooks.shtml

mcs37
Mar 25, 2003, 02:29 PM
Originally posted by vniow
Check out this link, seems like someone did it on an older Powerbook.

http://www.pbsource.com/contributions/readers/FlashRAM_and_PowerBooks.shtml

That's a great read! It was 2 years old and using 40 MB flash, and he saved 60-90 minutes of power by using the flash card as the boot disk rather than using the HDD. 60-90 minutes! Now imagine using a 1 GB flash card with lower failure rates (hopefully in the past two years the "burnout" problem mentioned in the article has been addressed somewhat). The cache could act as a great alternative to the HD as virtual memory, a fast bootup solution, and a better sleeping system. Using it as an HD cache would be doable if its failure rate was on par with RAM. And it could be mounted into the motherboard such that it could be easily replaced if it did burn out.

Mike

Eniregnat
Mar 25, 2003, 04:23 PM
Though not Apple, there is a company that makes mill-spec. and ruggedized computers. At least one of their models has a flash memory hard disk. This was some time ago and I remember that the costs were expensive.

I think that this is/was also the practice at some observatories that are placed at high altitudes where use conventional hard disks tend to fail.

Eniregnat
Mar 25, 2003, 04:30 PM
If one completely removed the conventional HD and replaced it with some sort of solid state drive, its durability and tolerance for environmental changes would also improve. One of the reasons that I love my eMate and my QuickPad Pro is that they no moving parts (less hinges), long uptime, and I can use them in almost any terrestrial environment that I could survive in.

When we look back at this thread, if we ever do, we will wonder how we survived in such a primitive world.

benixau
Mar 25, 2003, 04:53 PM
here is a link to some companies that sell solid state hard disks:
http://www.bitmicro.com/
http://www.m-sys.com/index.asp

this next one provides a list of most of the manufacturers i have missed
http://www.storagesearch.com/ssd.html. it is on the right of the page in a yellow box

enjoy!

mcs37
Mar 25, 2003, 05:01 PM
Originally posted by Eniregnat
When we look back at this thread, if we ever do, we will wonder how we survived in such a primitive world.

LOL, agreed on that one. My children are going to say, "Dad, you had storage systems consisting of platters of disks spinning at high speeds? So moving parts. Wow, that actually works!" Then he will turn on his 100 THz (?) Quantum PowerBook with Airport Steroids Super Extreme networking and 100 TB solid-state storage device with 100 ns access times.

And we'll have to say, yes, that's what we had until so-and-so invented a better way.

NavyIntel007
Mar 25, 2003, 05:03 PM
Originally posted by crapple33
Yes! This is a great idea! For awhile I've thought about how great it would be if we could have completely flash hard drives. Everything would be sooo fast. But since right now we're not at that capacity yet, this would be a great way to start. The largest flash card I know of right now is 1 gb, but at the rate things are going... Who knows?

The largest IDE flash hard drive I've seen is 2 GB

mcs37
Mar 25, 2003, 05:10 PM
Originally posted by NavyIntel007
The largest IDE flash hard drive I've seen is 2 GB

It looks like bitmicro.com has one up to 77 GB. Now one can only imagine how many thousands it costs. But hopefully within a few years we'll see some standard drives that are flash. I would love having a powerbook with 1-10 GB primary drive flash and 60 GB pure data files.

Mike

Eniregnat
Mar 25, 2003, 05:47 PM
It looks like bitmicro.com has one up to 77 GB.

I think that's for a RAID configuration.

The formfactor that I think most are thinking of is here (http://www.bitmicro.com/products_acedisk.php). (A link with in benixau's bitmicro link above.)

As we look at how ridiculous a 77gb flash drive would cost; I recall a bit of hilarity that a friend and I once got into.

As a technoweenie teen- somewhere in the 90ís, the debate of a tera byte drive came up. At the time, using the drives that we knew about, we calculated that the disk would be about three feet in diameter (no stacked platters) and that it would take a few hours to get up to speed. We figured that it might also double as gyroscope. We couldnít stop laughing, especialy when we guessed at what the access times would of been.