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IDE RAID Examined
Bender writes "The Tech Report has an interesting article comparing IDE RAID controllers from four of the top manufacturers. The article serves as more than just a straight product comparison, because the author has included tests for different RAID levels and different numbers of drives, plus a comprehensive series of benchmarks intended to isolate the performance quirks of each RAID controller card at each RAID level. The results raise questions about whether IDE RAID can really take the place of a more expensive SCSI storage subsystem in workstation or small-scale server environments. Worthwhile reading for the curious sysadmin." I personally would love to hear any ide-raid stories that slashdotters might have.
IDE can only handle one or two hard drives per channel, which makes the cabling a real nasty hassle as opposed to SCSI-based RAID.
Even those so-called rounded cables can clutter the hell out of a tower case if you have a 4-channel RAID controller.
In my case it's the Adaptec 2400A four-channel, with four 120GB Western Digital hard drives, RAID 1+0.
their big old file server had 5 hard drives in it, but was only using 1 in windows! Being the smart boy that he is, he dutifully shuts down the machine, removes one of the drives, puts it on the broken machine, formats and loads windows on it.
So how did he decide which of the 5 drives he was going to pull ?
Oh. My. God.
:P]
I let out a yelp when I got to
puts it on the broken machine, formats and loads windows on it *
One of the things that really chaps my ass, more than anything else, is people asking my advice (and they do so specifically because of my experience in whichever field they're inquiring about), patiently listening to what I have to say, asking intelligent questions... then doing something completely or mostly against my recommendations.
More often than not, something ends up going wrong that would/could not have occurred had they followed my advice in the first place, and then I hear about it.
It sucks the last drop of willpower from my soul to hold myself back from saying "I told you so!" and charging them a stupidity fee. It's tempting to do so even to friends, if/when I get sucked into the resulting mess. [Hear that, Jared?
* Linux zealots: For a more warm-and-cozy feeling, disregard the first eight words of this quote.
Thats bullshit. Post some links to benches that back that up.
Two 80GB WD special edition drives in RAID 0 (7200RPM, 8mb cache) rarely burst over 90MB/s. They usually have a sustained transfer of ~50-65MB/s.
Additionally, your seek time is going to suck. I gaurantee its not going to be under 11ms. You cpu utilization during transfer will prolly be around 4% in the asolute best case senario and 11% on average. This is becuase, no matter what you think, all raid cards under ~140$ do the calculations for the transfers in software, not hardware. All you have is a controller card with special drivers. You wont come even close to beating the overall performance of a scsi 160 drive, or SCSI 160 RAID 0 setup.
Ummm, no.
Try getting sustained data transfer rates out of an IDE RAID under load. It won't happen. You'll stutter. *boom* goes your realtime process.
SCSI RAID, on the other hand, streams happily along with very little CPU load.
STOP . AMERICA . NOW
Using IDE Raid is like using a winmodem. Unlike with modems, where everyone has one, RAID has a basic educational entry point. I seriously doubt IDE Raid will ever overtake SCSI in any area where knowledgeable people are doing the administration.
I keep telling them to wait a couple of years, and we'll see who is wasting money.
Agreed. This is not always easy to back up with facts (by quoting mfgr specs, etc), but in both recent and long-term (10+ years) experience, my systems with SCSI drives have tended to fail less often, and usually less suddenly, than IDE.
Generally, in 24x7 server usage, a SCSI disk will run for years, then either slowly develop bad blocks, or you start getting loud bearing noise, and after powering down, the drive fails to spin back up. In the old days we'd blame that failure mode on stiction, and could usually get the drive to come back one last time (long enough to make a backup) by giving the server a good solid thump in just the right spot.
Background:
My first SCSI-based PC was a 286 with a 8-bit seagate controller and a 54 MEG Quantum drive recovered from my old Atari 500 "sidecar".
So yeah, you could probably spend your money on other things to get better performance, but that's entirely besides the point. What could you spend that money on to get better data reliability?
You apparently didn't read the article, and have no current experience with IDE RAID systems. Take at look at the sustained tranfer rates of the 3Ware system. They meet just about any SCSI controller you're likely to find when paired with good 7200RPM drives. The myth that SCSI is the only way to get reliable sustained transfers is just that -- a myth. SCSI's only advantage now is reduced cable clutter and having up to 15 drives on one controller, but who needs that many drives these days when 120GB drives are available for next to nothing?
In the end they will lay their freedom at our feet and say to us, Make us your slaves, but feed us. - Fyodor Dostoyevsky
I like reading the comments here, I am humble enough to know I can always learn something. But there's something I didn't see mentioned, in all these IDE RAID setups that people describe: can you have a hot spare disk? Hot spare is critical for data reliability. If you have a large RAID 5 or RAID 0+1 (not advised, always do 1+0, whenever possible), you can do the math and see how darn important it is to have the host spare.
What good it is to have a RAID 5 without a hot spare, when you can only guard against single drive failure? So, I really hope IDE RAID supports hot spare, otherwise I question the saity of mind of the admins who implement such solutions.
As for IDE vs SCSI drives, I have to say that I will always go with SCSI, as long as I am in a multuser environment where seek times are critical. Apparently (experience shows), if you put your database space on a RAID, seek times are critical for the performance of your application. In this context, I think this review/coparison would have benefitted from a real-life aplication's benchmarking, with a database hosted on the RAID.
Sigged!