Slashdot Mirror
RAMdisk RAID?
drew_92123 asks: "I've got a friend who does a LOT of video editing but is on a limited budget. He is currently using a raid array and while quite large, it's not as fast as he had hoped. I had an idea and wanted to know if there is a way to make it a reality, so of course I though of all the brilliant minds here. I have about a dozen Pentium II computers with 1GB of RAM. I would like to upgrade them to 2GB and throw in some gigabit NICs and create a 1.9GB RAMdisk on each one. Then I want to use one of the computers to RAID the RAMdisks together to be shared via Samba most likely. They are all 1U systems, with no HDD's, just a 64MB IDE flash disk. Any ideas out there?" Has anyone successfully put together such a system? How well did it work for you and are there any caveats that you would like to share with others who would do the same?
you want to fragment all filesystem access into super-tiny 1500 byte ethernet packet access to each of several hosts for a mere 20gb ram "filesystem"?
gig E does not perform that well on a single host. You'll -might- get lower latency than a cheap raid array but the thruput won't be any better.
why waste time with "RAID" anyways? this ram is all ECC ram and is non-persistent so there's no point in tossing that extra computation into the mix to make it worse.
Ever thought of just upgrading your SCSI controller? You can get RAID controllers that have insane amounts of RAM in them. That might patch up any access issues.
If your concern is extended duration throughput the multiple rack computers with ram *might* be an option, but most normal users wouldn't consider it due to the latency involved with going through the southbridge then the nic then the nic then the southbridge (of the other computer) then the north bridge. And that's just a one way trip.
Just don't shell out a bunch of money before you do a proof of concept.
~george
I completely second this. The costs of the hardware will not be worth it. I suspect that you would do a lot better adding disks to the array, creating another array, or upgrading the ram on the main machine. Although it sounds like a cool idea in concept, this is not a good idea if you're doing anything but playing arround with the tech. It does sound like a cool project, though.
[FlameSuit On] I'm sure you all will flame me for this but, I can take it.{/FlameSuit Off]
It is very likely that he is already using IDE or ATA disks, and that is part of his problem. When large amounts of data need to be transferred quickly, SCSI is what you need. There is nothing faster than 15,000 RPM SCSI drives connected to good RAID controllers that have large amounts of cache RAM. Nothing.
If you want high performance then you must use high performance gear. Yes, it does cost 5 to 10 times more than the IDE RAID solution but, there is a VERY good reason for that.
Ok, now comes the flames from the know-it-all masses who's experience is limited to home PCs and no-traffic webservers.
Sorry, but I don't think so.
RAM -> RAM across a network (assuming at LEAST 100mbit ethernet) will be FASTER than accessing a RAID of local disks. It's all memory to memory transfer at that point - no spin up, no seek time. The disk's may get close for a very long sequential write/read, where the multiple drives can actually come close to using the bandwitdh available via the RAID controller.
But for random access...no way. RAM 'seek time' is measured in NANOSECONDS, while even the fastest drive is in the miliseconds! RAM is over 1000 times faster!
How about a be- *bang!*
*smack* *thump*
*mass cheering*
Btw, it does seem to be a (disturbing) recent trend at Slashdot to try to troll whole stories, instead of just trolling comments. C'mon anyone who's taken even one networking or hardware class knows the speed heirarchy:
cache > memory > disk > network
And, with the amount of physical RAM drives out there (very few), you'd quickly realize that even a local RAM drive doesn't offer enough of a speed benefit to offset it's cost. C'mon editors, I know it sounds cool, but do you really have to post it?
Kurdt
I'm not anti-social. Just pro-technology.
Ahh, come one... Anyone who is crazy enough to want to setup a lan-based-ram-raid-array (Whew...) is certainly going to be sane enough to set up some sort of serious power backup.
Of course just to repeat and be redundant, the bottle neck will simply come down to the NIC card, a possible solution would be to install several NIC's and spread the load out... But this person would be much better off simply buying a system that will either (a) handle 24 GB of RAM, or (b) has fast enough disks to please him...
Of course a better idea might be to buy a system that would support both (a) and (b) and then set the system up to use the ram as a primary holding area for data, then flush to the (now faster) disk array...
Either way this person is still affected by "The Sickness" that we all seem to suffer from (More, bigger, better, faster....)