The Old Joel on Software Forum: Part 3 (of 5)

IDE RAID

Two questions...
1) I'm seeing a lot of higher-end consumer PC's coming with RAID 0 installed by default. Has anyone bought one of these? I'm wondering if they come with the huge warnings *I* would put about the dangers of striping (namely you're cutting your MTBF by the number of drives).

2) Does anyone know if there are any IDE RAID 5 solutions? I want to increase my storage at home, and I'm currently leaning towards a mirrored pair of 160 GB IDE drives, but wouldn't mind going with four 40GB in a RAID 5 array (I know, 25% less storage).

...and I've gotta go do some SCSI math again...

Philo

Philo
Saturday, December 27, 2003

The IDE RAID-0 solutions seem to be mostly aimed at the PC-hot-rodding "enthusiast" market. I don't think they know or care about the obvious data risks, they just want every bit of performance.

Luckily all the IDE RAID solutions seem to do RAID-1 as well, for a more sensible approach. I'm sure IDE RAID wouldn't be very popular with only RAID-1, so I'm glad all the RAID-0 knuckleheads are subsidizing my cheap RAID-1 setups. :P

Not sure about IDE RAID-5. Never heard of any manufacturers implementing it, that's for sure.

John Rose
Saturday, December 27, 2003

Yeah, hard drives are cheap enough to make RAID-1 fine. I actually got to the point of thinking of rebuilding my machine from the inside out, but I think I'll stick with upgrading CPU, video and hard drives, then looking at a new box later in the year.

Philo

Philo
Saturday, December 27, 2003

Philo,

These 3 articles might be quite useful for you:

http://www6.tomshardware.com/storage/20021112/index.html
http://www6.tomshardware.com/storage/20020813/index.html
http://www6.tomshardware.com/storage/20020830/index.html

jim
Saturday, December 27, 2003

Oh, and this recent one too:

http://www6.tomshardware.com/storage/20031128/index.html

This solution gives RAID-5 SCSI speed using IDE, but at a cost of only about 10% higher than standard IDE RAID solutions.

Check it out.

jim
Saturday, December 27, 2003

High end consumer motherboards come this days with RAID0 (stripping, basically if you lose 1 HD all data is lost), RAID1 (mirroring, after losing 1 HD the information is still intact) and RAID0+1 (nicely described as mirrored pair of striped arrays). I am leaning towards a 120GB RAID1 myself.

There are 2 reasons for choosing a RAID: fail-safe data and performance. RAID0 is not fail-safe while RAID1 has a lower performance due to the write penalty. RAID5 is a more expensive combination to alleviate those problems.

Anybody has experience with four 7200 RPM hard drives in the same box? I think they will need 2 cooling fans only for themselves.

coresi
Saturday, December 27, 2003

I've got four older 7200rpm SCSI drives in a box with two P3's - my box with a single P4 and one drive runs hotter.

Philo

Philo
Saturday, December 27, 2003

http://www.3ware.com for all your IDE RAID needs

Unlike most other RAID controllers and most of the ones that are inbuilt into the motherboard, the 3ware cards do the majority of the RAID processing in hardware, whereas others will take a slice of CPU time

Dan G
Saturday, December 27, 2003

Dan makes an important point.

These $10 RAID chips on the motherboard rely almost entirely on software to perform their RAID functionality. The system cannot be ignorant of their presence (as it can in the case of a fully hardware RAID) because the drivers are doing the heavy lifting.

RAID 5 is definitely alive and well in SCSI, but the cost is hard to justify for anything but servers. I'm curious about the RAID 5 IDE link that he just posted... I run a SATA RAID 1 120GB array for my desktop development, and it's fast. Not as fast as a fully hardware solution would be, but it's certainly never felt in the way (like a fully software RAID 1 solution does).

Brad Wilson (dotnetguy.techieswithcats.com)
Saturday, December 27, 2003

Thanks for the link to those 3Ware RAID cards. they look quite nice. And in relation, they do support IDE RAID-5, by the way.

For the record, I've been using an el-cheapo Highpoint IDE RAID card on my development server for a RAID-1 config. I'm sure it's not as fast as a more hardware-based RAID setup like the 3ware cards, but for what it's worth the Highpoint card+drivers have been an absolute breeze to set up and use. Nothing but smooth sailing...

John Rose
Sunday, December 28, 2003

My MoBo came with RAID but I never used it. The RAID channels though were in addition to the existing IDE channels, so I think my MoBo can support up to a total of 8 drives, or 6 if I want to use RAID.

The same cautions as everyone else about RAID 0... I know someone who just lost all his data, I presume it was because of RAID issues.

www.MarkTAW.com
Sunday, December 28, 2003

Adaptec make an IDE RAID-5 card, and very good it is too. It supports upto 128Mb cache in the form of an 168 pin SDRAM DIMM. I would strongly recommend the cache be invested in.

Running at RAID-5 on IDE means there can only be one drive present on each channel, on the Adaptec cards this is true at least. Something to do with IDE not being able to read/write to multiple devices on the same channel simultaenously I believe.

Anon
Sunday, December 28, 2003

That's true.

Serial-ATA makes a lot more sense for RAID to me.

Brad Wilson (dotnetguy.techieswithcats.com)
Monday, December 29, 2003

Personally I'd avoid a software solution for RAID level 5. It can be handy for RAID0, maybe even for RAID1, the performance gained by utilising two (or more) disks instead of one is distinctly noticeable.

I think the added overhead of the XOR-like operation RAID5 uses might eat into that somewhat. Be warned, though, when one of the 80Gb drives in my RAID5 set went down, it took the ATA 2400A card around 72 hours to write the data to the new one and get me back up and running (to be fair the set was full to bulging). The equivalent Serial ATA card is the Adaptec 2410SA.

Anon
Monday, December 29, 2003

I don't know if this an option for you, but an alternative to consider is a slightly older SCSI RAID solution. It won't be state of the art but I bet it would come close to or even exceed the performance of a new IDE RAID set. You could pick up an older Intel RAIDExpress card and a number of, say, 36Gb SCSI2-UW drives on ebay for a fair price. Those Intel cards are great, support RAID 0,1,5,10,50 and 128Mb cache via an EDO SIMM (remember those?).

You can pick up slightly older (say SCSI2-UW or even U160) SCSI drives quite reasonably these days.

Anon
Monday, December 29, 2003

I used to be a RAID enthusiast, but I'm a bit disenchanted with it, basically because of the added complexity. When something goes wrong with a disk, the *last* thing I want to do is fool with the RAID controller.

I'd suggest cold-copying as an alternative (*). Either cold-copy to a second hard-drive on the same machine, or set up a simple backup server with a fast link between the two and differential copying (eg, rsync).

With this method, recovery is dead simple: you toss the failing disk, put in the clean disk and reboot. With the networked version, you get a new disk, copy all the saved data to the new disk and reboot.

* What I actually do is RAID 1 the disks and cold copy the data to a network disk.

Portabella
Tuesday, December 30, 2003

I'm not sure what you mean by fiddling with the controller. When the disk in the RAID5 set died all I had to do was plug in a new drive and voila, the management software kicked on when I booted the machine and did the rest, complete with pretty progress indicator.

Something else I forgot to mention, though, the RAID card dying can leave you in a bit of a pickle. RAID sets are mostly *not* portable between cards of different manufacturers. So you may want to have a redudnant RAID controller as well - extra expensive tsk tsk!

Anon
Tuesday, December 30, 2003

> I'm not sure what you mean by fiddling with the controller

Typically I have to dig out the RAID documentation when a disk dies.

And, like you say, if the controller itself has a problem, or encounters something it doesn't know how to handle.... well, the reason I set things up the way I described is to make everything idiot-proof and not even go there.

Dig: I understand that when the controller works well, it's a just-drop-in-another-disk-and-go no-brainer. It's the catastrophic case that I worry about.

Portabella
Tuesday, December 30, 2003