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Why Not Solid State Hard Drives?
waterlogged asks: "I was just wondering if anybody has heard of a cheap ram based network drive? Seems to me with the ram prices being at about US. $12.00 for 128 megs that someone hasn't developed a battery backup version of this to plug into a network or even a bus. A gig worth of 8ns seek time storage for $120 anyone? That would just about eliminate any wait in loading programs."
BigSlowTarget asks: "There are some previous articles on Slashdot about vendors selling solid state drives, but they all seem to be quite expensive - particularly given the slide in the cost of memory. Has anyone hacked together a solid state drive to take advantage of $60/GB memory prices? I'd really like to be able to boot and run at solid state speed without spending thousands."
Jah-Wren Ryel asks: "In case you haven't noticed, RAM is incredibly cheap, you can put a gigabyte of PC133 RAM into your machine for less than $60. A year ago, that would have cost more like $600. So now it is feasible for one to have a 10-15GB RAM disk, except for one thing - most motherboards won't support more than 2GB total (4 dimm slots x 512MB per dimm). It seems like it wouldn't be too hard to design a PCI card to hold 20-30 dimms and make that available through a hardware windowing scheme (like EMS/EMM back in the old 16-bit days). With the right drivers it could be used as a big RAM disk or for buffercache. Is there such a product out there? The closest I have seen are solid-state disks that sit on the other end of a scsi bus, are too expensive, and aren't anywhere near as fast as a PCI implementation could be."
So what technical details (and the issues of volatile data and price) may be preventing the construction of RAM based drives, and is there anything else that may be preventing some entrepreneurial soul from bringing such a thing to market?
(heh. oops.)
Cenatek seems to be on a good track with these. They offer a PCI card with a handful of DIMM slots, a slap on rechargable battery panel, which holds enough power to run a connected hard drive of appropriate size which will dump the contents of what is essentially a RAM disk, in the event of a shutdown or power loss. A little spendy still, for consumer use, but to see something like this backend busy websites, or store database file structures would be pretty slick.
- billn
Cenatek may make exactly what you're looking for. It's a PCI card, and uses standard SDRAM sticks.
From their site:
The Rocket Drive stores data in memory modules (standard dynamic random access memory, or DRAM) rather than on magnetic media.
RAM is now cheaper when it comes to memory-per-unitofcurrency than hard drives.
According to pricewatch, a 40 gig hard drive is $78. Let's say $120 for a good one. That makes RAM 20 times more expensive, at $60/gig.
It's still really cheap, but let's not get crazy. :)
Sometimes it's best to just let stupid people be stupid.
Your CMOS is something different, actually. Most computers use "DRAM", which needs to be "refreshed" often, or it'll "lose it's charge"... ROMish stuff is SRAM, which doesn't need the stupid refreshes... But it's more expensive, so a a couple gigs of SRAM is sorta out of the question. :(
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suwain_2
Argh. Forgot to preview. Here's the guys you mean: http://www.soliddata.com/
Any sufficiently well-organized community is indistinguishable from Government.
You are right. Cliff is wrong.
Given his figure of 128MB for $12, that's 10.66MB per dollar.
From western-digital.com I can get a 40GB 7200RPM UATA/100 caviar harddrive for $117.00. That's 341.88MB per dollar.
This puts harddrives into the lead by a factor of 32. So, until it's at the point where 128MB of RAM costs $0.375, harddrives still have the lead.
Justin Dubs
CMOS only consumes power on state changes. DRAM needs to be refreshed every few ms. Thus, the battery power required for DRAM would be much greater than that used to hold you CMOS settings in BIOS.
I'll be damned if I can find anything at ATTO's website, but they used to make the SiliconDisk II, essentially a SCSI hard drive made completely of DRAM (yes, it has power outage protection).
SSD's have been around for quite some time. Compaq had several commercial offerings based on Quantum's SSD. There are also several no-name companies that manufacture solid state drives (Memtech being just one: http://www.memtech.com/Prodinfo.htm).
We actually got our Alpha vendor to let us try an SSD for 30 days. The drive was fast, but we found that we quickly saturated the controller (something a couple U160 drives can easily do). In that regard, it wasn't that fast at all.
And, as has been said in other posts, it's not really economically fesible. We tested a 3.2GB SSD last Christmas that cost $25,000. For that application, we thought it was a good fit. But if you're concerned about capacity, we just bought some 180GB drives for our SAN for about $5,000.00 each.
While the RAM and disk capacity available now is amazing, I don't think we'll ever see the dollar/cost ratio for RAM beat the dollar/cost ratio for disks.
In 1994, which I had a 486/DX2 66 (which came with 4MB Ram), I bought 16MB of RAM for $560.00. Quake was 15MB, so I could load it into a ram drive and play from there. Guess what? It wasn't noticably faster than my IDE hard drive, but Windows screamed. =)
"All I ever wanted was to see Larry Wall give Bill Gates a Perl necklace."
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I hope this was helpful.
I read the internet for the articles.
I agree - even a SDRAM controller right on the PCI bus can't be as fast as the system's main memory.
Linux, FreeBSD, and MacOSX (I dunno about Windows) all have excellent VM and file system caches (sometimes they're tightly integrated). If you have 4GB of RAM in your system, and your running processes have 64MB resident, then it's like having a 3.94GB RAM disk. That is, of course, unless you routinely access more than 3.94GB of files.
This is why having lots of RAM is good, even if your processes don't use much.
It's not prefect - I know that on FreeBSD 4, for example, if you have zillions of small frequently used files in the cache, and then you do a big tar, all those important little files will get pushed out of the cache in favor of the new file, which might only be accessed once. Also, the kernel will swap processes out to make room for file system cache, and there aren't a lot of knobs for tuning all of this. EG I don't think you tell the kernel "keep *all* my processes resident, even if they're idle... no really, I *do* have enough RAM!"
Anyway I just don't see any use for standalone RAM disks. There are very few real-world applications that need *deterministic* 1ms seek times. If you rely on the OS you will generally get the best performance.
Aside from being expensive...
Flash is slow to write to.... and is limited in the number of writes. Flash wears out.
I read at a Flash RAM manufacturer's website that their devices reach MTBF in one million writes. If a sector gets written to once a minute in average, that's about two years. Too little.
Which is exactly what Western Digital did with their 100 Gig caviar drive. They've taken advantage of cheap dram to pump their cache up to 8MB from the usual 2 MB. The result is their 7200 rpm drive is outrunning 10k rpm drives and is quieter as well.
More info on the Western Digital drive is available at storage review.