Hello,

I am looking for advice on the purchase of an IDE RAID card for linux. The RAID card would be for our server, a Mandrake 9 box, and would perform RAID 0 (mirroring). We are essentially considering Adaptec and Promise. Not sure which is better for linux.

The other issue, is how hard is it to set up RAID on an existing linux installation? Is it easier to start over, or is it fairly straight forward? The card would obviously need to be installed (driver) before I switch the hard drives to the RAID card (so it will boot). I'm not sure how much work this involves.

Any suggestions or thoughts? Any info would be great.

RAID1 (mirroring) </nitpicking>

Software RAID1 is easy to set up on an existing system. The hardware-ish ATA RAID should be almost as easy, exept you would probably do the drive sync at bootup (in the BIOS).

This topic is popping a lot lately and I for one would like to get a solid answer on the performance difference between s/w RAID and 'simple' ATA RAID. My understanding is that the ATA RAID cards are merely IDE(ATA) comtrollers with a bit of extra code for management at the BIOS level. Any live resync would be controlled by software on the host machine.

Don't get me wrong - the ATA RAID cards are great for people using an OS that won't do software RAID (Win9x) and are plug-and-play-ish in that environment. I'm just not sold that there's any real benefit in performance or setup over Linux RAID tools.

If you have a decent budget, both Adaptec and Promise offer higher end RAID cards with onboard RISC chips that do all the gymnastics (ie resync) and keep that load off the CPU and out of the bus.
* Adaptec ATA RAID 2400A claims to be supported by SuSE 7.1 so I hope that the kernel support is readily available by now.

As for Promises' ATA RAID - they were a bit fluffy in the past with drivers for Linux, and they don't brag about the range of OS's they suuport on the site so I'll leave that to the reader as a search project.

There was a recent article on Slashdot about this. 4 cards were compared: Adaptec, Promise, 3ware and some OEM chipset. The high points were that the Promise is the fastest, but it uses quite a bit of CPU--like up to 24% during 1 test. The Adaptec didn't win any of the performance tests, but it did quite well overall and had very low CPU overhead.

The CPU overhead is one of the important things to consider, in my not so humble opinion. If you have other processes on your server, such as a webserver or an MTA, you don't want your disk slowing them down.

Lastly, why hardware RAID for mirroring? Most of the newer distro's have software raid built in. RedHat's installer makes it very easy to configure it at install time. Even if you don't want to reinstall, its really easy to set up a raidtab file, do a mkraid, mkfs and go.

Found the test report - http://tech-report.com/reviews/2002q...d/index.x?pg=1

The sad part is that this test was done on an XP setup. I would like to have seen any optimizations that vendors could have refrerred to the authors in the time since the test was published. Some of the results could be due to a configuration issue.

As for the CPU usage - it looked a lot worse than it appeared on the graphs. What looked like a huge difference was only about 3 - 4 percent difference.

Plus the article mentioned what I failed to - the 3Ware card. They were one of the first to offer a real ata RAID card for Linux users. It looked like a pretty strong card overall.

At least they mention Linux on the list of supported OSes. I had forgotten about which OS they tested on.

The real kicker to the original poster is why IDE? The drives are nortoriously more prone to failure than most SCSI drives, and don't perform as well in a multi-user environment due to the size of the command queue. I know that all he wanted to do was mirror, but I still hold out for SCSI in a server environment.

The primary reason for most users is the budget. SCSI drives are... (memory failure here... had to look it up) about 3 or four times the price. Add to this the cost of the controller and RAID card and you're gonna spend some money. In the short term it's pretty expensive.

In the long term I still think SCSI's the best way to go. You're not going to match the speed and reliability of a SCSI with ATA - it's always falling behind. Then there's downtime - SCSI drives have better warranties, longer MTBF. Real disconnect from the chain allows SCSI drives to be command queued and left to finish its task while the bus can go and talk to the other drives. Have a look at a 5 year old server with SCSI drives. It's still gonna be a pretty good server. Now have a look at a 5 year old IDE server...

Sure a Yugo and a Toyota are both cars with four wheels....

Wow, lots of things to think about. I don't want to do software raid because as I see it, it would hog more of the cpu. This box IS a webserver/mysql server, as well as doing ntp/dhcp/bind and a few other services to our small lan (<25). Why IDE? Primarily cost. We are a small newspaper, and we can't afford SCSI drives.

If the budget were there, I would most definitely go SCSI, but that's not the issue here. This machine isn't brand new either. It's a 800MHz PIII, w/ 256 MB RAM, and 40GB ATA hard drive. I want mirroring for fault tolerance, obviously. I already have an identical hard drive, so a single raid card is obviously cheaper than 2 brand new scsi disks AND a raid card.

I want to squeeze every clock cycle I can out of the processor. Our website is CGI/db intensive so CPU is an issue.

Which is the least CPU intensive routes, and which are the easiest to impliment? RAID on linux is completely new to me (duh, right?).

Thanks for the comments, BTW.

tisource, RAID 0 is striping and RAID 1 is mirroring. You were not clear.
Which RAID level did you meant?
What is the server going to be used for?
How many hard drives are you going or thinking to use?

A server that is using RAID should be using level 5. Level five gives you striping, near fault tolerance, and hot swapping. It doesn't matter what interface. SCSI hard drives are prefered because much lower accessing times and higher throughput. IDE hard drives can be used but they have wire length limitations. You may look into Serial ATA hardware to minimize wire length limitations and throughput problems. Just make sure you have enough power left over after powering the motherboard. The motherboard does consume a lot of energy. If the 5 and 12 voltages drop your hard drives won't function correctly or up to their maximum speed.

Benchmarks that several people read doesn't give a good indicator in real world conditions. It is best have you, the adminstrator, of the server to benchmark the servers by giving it requests to see the effects on the hardware.

RAID shouldn't be to hard to setup if you have gone through the controller's BIOS setup to make the RAID arrays. Mandrake gives you good tools to add a hard drive very easily.

IMO, the linux drive should be seperate from the drives that are going to serve serveral people.

I will be performing mirroring. SCSI is not an option at this point. Our budget is tight. I want mirroring for fault tolerance.

IDE's have their limitation, but they are more than sufficient for what we are doing. This server performs the following services:

- Web (apache + mod_php)
- Database (MySQL)
- Time Sync (NTP+Daytime)
- DHCP (< 25 computers on the lan)
- SSH/Telnet (Mostly for me, admin)
- FTP (ProFTPd, strictly for web transfers (me only))
- DNS (BIND 9.2.1, non-authorative, for our LAN only)

I'm not concerned with performance, as much as stability and compatibility with linux. If I had the money, I would go with higher end hardware, but that is not an option at this point. We just want to ensure we don't lose data. That's the issue.

Throwing SCSI out of the picture, which RAID card (for mirroring) is best for linux? Which is the most stable? Which is the easiest to set up?

I haven't setup professional RAID controllers or software RAID controllers though controllers with onboard processor and memory should help for database servers. There are hard drives such as Western Digital that has 8 megabytes of cache that should help even more for a random accessing storage such as database storage and as well as for video and sound. Just make sure you include a tape drive in the system and cool the hard drives down.