RAM Disk Puts New Spin On the SSD

theraindog writes "Although the solid-state storage market is currently dominated by flash-based devices, you can also build an SSD out of standard system memory modules. Hardware-based RAM disks tend to be prohibitively expensive, but ACard has built an affordable one that supports up to 64GB of standard DDR2 memory and features dual Serial ATA ports to improve performance with RAID configurations. And it's driver-free and OS-independent, too. The Tech Report's in-depth review of the ANS-9010 RAM disk pits it against the fastest SSDs around and nicely illustrates the drive's staggering performance potential with multitasking and multi-user loads. However, it also highlights the device's shortcomings, including the fact that SSDs are more practical for most applications."

Comments

What I learned from the article

[Wonko the Sane]

• Most tasks are not disk IO-bound
• Despite the fact that this device uses DDR2 RAM running at more than 6 GB/sec, it can not saturate 2 SATA interfaces
• Why bother?

Re:What I learned from the article

[Wonko the Sane]

But are you really getting your money's worth from this device?

DDR2 is an order of magnitude faster than SATA. Looking at their numbers, the internal controller is limited to about 400 MB/sec. That is pretty mediocre.

Re:What I learned from the article

[Forge]

This brings up an interesting idea.

What if the ramdisk function was moved into the motherboard chipset? This would achieve 2 things:

1. It would dramatically cut the cost of a ramdisk. I.e. The cost of the entire motherboard might go up by $5 or so.

2. It would eliminate that SATA bottleneck, allowing ramdisk to run at full RAM speed.

If you then figure out a way to have this data loaded to the ramdisk from a hard drive at poweron (or get realy clever and mount a flash chip on or near each DIMM which takes a backup of that DIMM, just before powerdown.

Re:What I learned from the article

[Ed Avis]

Why would you spend your money on this device instead of just buying the equivalent amount of RAM and putting it on the motherboard where the processor can access it directly? Even if you had to upgrade to a more expensive motherboard you'd still get way better price-performance by doing that, rather than crippling the RAM by putting it on the other side of the SATA bottleneck.

If you insist on having a 'disk' you can save files to, well, all OSes support the idea of a RAM disk...

Re:Why are these always so expensive?

[tulcod]

what bothers me most is that these RAM disks aren't even much faster than intel's SSD. considering the price, i think that's quite a shame. long live competition.

In summary

[Max Romantschuk]

Skimming the article, I'd summarize as follows:

Real world performance not radically better than fast traditional HDs or SSD solutions, and you can't power off your PC for the night. (Unless you backup to flash every night.)

I'd say this is a niche product, but could be a very good one for a chosen few applications.

I RTFA and now speculate

[moteyalpha]

It seems that with a little firmware it could be coaxed to do some content addressability. Considering that it is 10x faster inside than the peak of the SATA interface. It seems to me that there is a lot of potential. I always liked the ram disks when they were popular ISA cards and this could be the thing that could use the full power of USB 4.0 [sic]. Applications could be changed to take advantage of this speed. If lists and SQL databases could be sorted on the drive without CPU overhead, it could be very useful.

Re:Great for swap and /tmp

[Ginger Unicorn]

The whole thing is pointless - why not just put 64GBs of ram in your PC and let it fill it up with disk cache. This makes no sense. If you compare this thing to just putting the RAM in your PC there are NO upsides. The data is vulnerable, it's massively expensive and an inefficient use of the RAM modules. Madness.

Re:Great for swap and /tmp

[ustolemyname]

I wouldn't say "no" sense. It's battery backed up + connected to a compact flash slot, so when the power goes out it starts backing up your data to permanent storage.

My apologies - forgot I wasn't supposed to RTFA.

Good idea

[ledow]

My university used RAM disks back in the day - it was the only way to get decent performance on older machines. The computers didn't even have hard disks in. My brother (who went to the same university) has a story where he sped up his large FORTRAN compiles by a factor of 10 just by working out how to use the RAMDisk (which was only ever used by the PXE-style boot procedure and then hidden from the OS) for his own purposes and people couldn't work out how he was doing it because he still took stuff home and brought it in on floppy. This is a nice hark back to those times.

The killer, however, is the price... the price of a PC, basically, before you add the RAM. If you're REALLY serious, you'll have machines that can just take the extra RAM directly and do this in software. If you're not willing to pay that much, well, nothing will work for you but a few bits of extra RAM and a fast SSD for the same price won't go amiss. However, if you occupy the middle ground... this still doesn't seem worth the effort. It'd be cheaper to just buy an SSD, some extra RAM for cache and maybe even a cheap PC to throw it all in (if NanoITX supported 8Gig chips, this device could almost be made obsolete overnight).

The interconnect too - yes, it emulates a SATA drive but it emulates two as well and fails to do anything significant with them. So you'd need a RAID0 setup, with independent SATA setup, and an expensive device, with lots of even more expensive RAM just to be a fraction of a second quicker than an off-the-shelf SSD in the same machine. The people for whom it's worth it won't want to be bothered with all this.

The CF Backup feature is fantastic. I love the idea. But 20 minutes is a long time to wait if the battery is only four hours worth when it's brand new (four hours? At least 24 would have been useful and given you a chance to actually do something with it). You would want to be backing up anything this thing held anyway, so you don't really gain anything because the CF is the most inconvenient backup because of its manual nature.

I can't see a situation where 64Gb of fast storage is worth that amount of money + time + hassle + 64Gb of RAM + potential firmware problems + interface cabling + ... The bottlenecks in anything serious are going to be elsewhere.

Re:Great for swap and /tmp

[cyberjock1980]

If you compare this thing to just putting the RAM in your PC there are NO upsides.

Ok...
1. Find me a motherboard that has 8 RAM slots that doesn't require expensive ECC and/or Registered memory
2. Find me a computer that can boot from it's own RAM drive.
3. Find me a computer that can use a RAM drive that can be persistent through reboots without having to save the contents to something else.

I have several of these, and I run a power cord that is normally used for one of those SATA/IDE to USB kits in the back of my computer to power my box.

You don't think about all of the uses that this thing offers.

Son of iRAM

[(H)elix1]

I got one of these in our lab, and can answer questions on it. Had both units... the 6 slot version and the 8 slot version. This thing is the spiritual successor of gigabytes's iRAM. It takes bog standard DDR2 RAM as storage and lets you connect it as a SATA drive.

A few of the things it improved on the old iRAM.

*DDR2 supported ram, with 6-8 slots, taking up to 4G sticks.
*A fair sized battery.
*A CF backup slot.
*RAID friendly, multiple SATA ports on 8 slot model.
*Uses 5.25" bay rather than PCI slot.
*ECC

First off, no special device driver was needed - the drive was OS agnostic. Every mainboard and controller card I used saw it the device like any other SATA hard drive you might plug in.

The RAM slots take bog standard DDR2 RAM. The documenation mentions speeds of 400/533/667/800 are all supported. Benchmarks with 533 and 800 grade RAM produced identical benchmarks, so faster RAM does not appear to have any impact. I also mixed and matched faster and slower DDR2 modules without issue.

Just like most mainboards, the RAM needed to be installed in pairs if over one stick was used.

Unbuffered ECC or non-ECC modules are both supported. Registered RAM was not. I tried to pull eight 4GB sticks from one of my Sun boxes to give the 'full montey' test. No joy. Had to stick with the far cheaper RAM.

There was an interesting option for these who wanted to have ECC but used 'regular' non-ECC RAM. Eleven percent of the memory could be reserved for error correction. Again, all hardware based - just move a jumper. Performance metrics between ECC and 'simulated ECC' had negligible differences.

The 8 slot model has two SATA ports. By setting a jumper, you could have the entire RAM capacity as one large drive on one SATA port or split it as two independent drives. If you splid the drive you had to have an even number of RAM sticks installed. Another jumper would dumb the interface down to SATA1 speeds rather than SATA2. Never tested that....

Did test RAID-0, however. (grin) The synthetic benchmarks don't hit this device's sweet spot - database usage. Reads are fast. Writes are just about as fast. The RAID controller really makes a difference, as my 3Ware card performed significantly faster than with the mainboard based RAID. Using a EVGA 780i mainboard, it was not crushingly faster than a trio of velociraptors.

For anyone who has installed XP, you know the wait between hitting the 'workgroup' and the first reboot? Just over two minutes. By far the fastest install I've ever done. The OS also started faster than any other disk or SSD system I've used.

The CF bay was a nifty option. The question came up - what if I want to shut my machine down overnight? You can. If you have a CF card with more capacity than your RAM, it will back up the disk image automagically. You can also push a button to back up the current 'drive image' to CF, and another to restore the image. (I was able to go back and forth from Linux and Windows very easily).

Anyhow, tis a fantastic high speed scratch disk or OS disk when write speed matters. For those of us who already maxed out RAM, this covers the gap between RAM drive sharing RAM with the mainboard and fast disk.