Slashdot Mirror

exactly. I did the googling ... try this 2-20GB SCSI RAM drive, or similar products.

exactly. I did the googling ... try this 2-20GB SCSI RAM drive, or similar products.

SolidData sells solid state drives. Mountable by SCSI or FiberChannel (think SANs).

Anyhow, their website has info on how the data is backed up.

What characteristics do you want? There are two major types of solid state drives -- battery-backed ram, and flash ram. Both are expensive and small. Only one is fast.

My requirements were essentially (1) no moving parts, (2) affordable if not cheap, and (3) small. I settles on one of these. Debian is fine on 128MB, with 512MB of ram and no swap. Performance, it should be said, sucks. The next step up, for slightly more performance, much more capacity, and a whole lot more cost, is here; but I wanted to avoid using a case that needed drive bays, plus I haven't pockets that deep.

Neither of those is likely to be what you want for a database system, though. You're probably more in the market for a bunch of ram and a battery, unless your primary concern is reliability. If speed is the goal, you want this, or, for more capacity and more money, this. Note that I haven't used either extensively, and in playing around with the rocket a little, I was surprised just how much of a bottleneck PCI became. Also, the rocket doesn't have a battery... so really, unless you have a board with 8GB of memory, and you just need another 8GB of low latency space, it's not such a great deal today.

If you fit into any of the niches above, solid state is wonderful. It's always more expensive than you think, though. And for any database systems I've dealt with, a disk is without question the way to go, perhaps with more memory on board. But if you want any further tips, I'm glad to help.

I think we'd all be better off when solid state, non-mechanical disks become commonplace.

A company named SolidData sells solid state "drives".

While profiling a high-volume qmail server with fast mirrored drives, I noticed that I could get at least an order of magnitude sustained mail throughput by eliminating the fsync() system call, which essentially forces the disk subsystem to stop whatever else its doing and get a few specific blocks all the way onto disk. You can't run it in production this way, as the SMTP RFC specifies that the mail must be actually on disk before the server can claim that its done.

The problem is that magnetic-media drives can only seek a few hundred times per second. Regardless of their claimed sustained throughput, if you are writing a bunch of small files to disk, you are completely dependent on the seek time of the drive.

But mounting a magnetic-media-based ext3 with data=journal and the journal on an NVRAM block device would essentially use this as a trusted write-cache. Linux will return from the fsync() system call as soon as the data is in the journal, which could happen instantly on an NVRAM disk as there is no seek time. It then reads from the journal in its spare time, sorts it to minimize seeks, and writes the data out to disk.

I suspect that this should offer roughly the same speed as eliminating the fsync()s entirely.

I was looking into ordering a similar product to test this. I found:

• http://www.imperialtech.com/products_megaram35.htm
• http://www.platypustechnology.com/20qikdrive.asp
• http://www.mncurtis.com/curtis/CurtisProducts/Clip perTwo.htm
• http://www.soliddata.com/products/datasheets/e100_ specs.html

...for quite some time. Still, as others have pointed out it's still not the cheap solution. But if you need fast access to data, it is really neat. I have no affiliation with SolidData but I worked for a company that had their equipment. Well thought out design. The units had their own UPS and a regular hard drive inside the case. In the event of a power failure the entire contents of the RAM disk was copied to the hard drive before the unit shut down. Likewise, when it would power up it had to copy the contents of the hard disk back to RAM before it was available. Other than that, as far as the OS was concerned, it acted just like another hard disk.

Argh. Forgot to preview. Here's the guys you mean: http://www.soliddata.com/