What Kind Of Software RAID Are You Running?

ErikZ asks: "Lately, I'm having issues with my RAID. Specifically, closed source drivers for my RAID card that only support Red Hat 9. So I've decided to Ebay the card, and try to figure out how to turn 4 SATA drives into a software driven RAID 5 setup. Yes, I know I'll lose all the data, and I'm not worried about it. Finding a 4 port (or more) SATA controller card, that's well supported under Linux, has been difficult. Everyone wants to slap on their own RAID chip and charge you another 100$ for the pleasure. Where can a guy get a highly recommended, well supported, 4 port SATA card for Linux? The Rocket 1540 cards have vanished off the face of the earth. There are a few motherboards out there that have 4+ SATA connectors on them, but they also add RAID and some other cutting edge features that aren't well supported under Linux. So, I thought I'd try another route and ask Slashdot: What are you using for your Linux software RAID needs? What do you suggest?"

Comments

it doesn't really matter, does it?

[Anonymous Coward]

First of all, don't use software raid when you can get, e.g., a nice 3ware card that works well.

But, sometimes software raid is fun to play with at home. For that purpose I just have a couple Promise cards stuck in my machine, each with two SATA plugs. Works fine.

If you're using software raid, it seems to me it doesn't really matter what kind of hardware you are using.

Uhmm, what's your problem really...

[joto]

Lately, I'm having issues with my RAID. Specifically, closed source drivers for my RAID card that only support Red Hat 9. So I've decided to Ebay the card, and try to figure out how to turn 4 SATA drives into a software driven RAID 5 setup. Yes, I know I'll lose all the data, and I'm not worried about it. Finding a 4 port (or more) SATA controller card, that's well supported under Linux, has been difficult. Everyone wants to slap on their own RAID chip and charge you another 100$ for the pleasure.

But can't you just use your raid card as a SATA card, and ignore the raid functionality? Why do you absolutely need it to be non-RAID? I'm sorry, but I'm having real trouble understanding what's the difficulty here...

Re:I'm using md, aka Linux Software Raid

[kzadot]

Unless you want to boot, in which case you will need a seperate boot drive because the BIOS cant load the kernel off a software raid.

Which defeats the purpose, as the performance gains from RAID are going to be greater on the system drive (swap space, loading programs, libraries, program resources etc) than on the data drive, which is typically multimedia data where performance isnt a factor, as when you save it, your download speed is the bottleneck, and when you play it, the multimedia files have set bitrate.

I just dont get software raid.. Its the system drive that has the most to gain from RAID yet software raid doesnt work on system drives. Who gives a shit if your mp3 drive is faster it only has to deliver a couple of hundred kbps.

FUD

[adolf]

On my systems, I have a software RAID-1 "boot drive."

If one drive in the pair fails, things keep ticking along smoothly. They're really just identical partitions with identical data on different disks.

LILO merrily writes boot code to the array without episode. Meanwhile, the machine's BIOS is happy to boot from disks other than primary-master, all by itself.

I've booted the system after randomly unplugging devices. It works just fine.

Why do all of you 3ware goons think that the world wants to buy hardware which offers no clear advantage over having no hardware at all? (As if I want to add -more- potential points of failure to my systems . . .)

Re:FUD

[GoRK]

The ol' software raid 1 boot trick depends highly on the behavior of your BIOS under a failed drive condition. This is not the same thing as you get when you unplug a drive. Some BIOS may boot fine; some may not boot from the 2nd hard drive if the first is still attached and failing. It may also depend on how your drive has failed. If the drive electronics are failed and shorting the wrong pins on your IDE controller, then you may not get past the drive detection code in the BIOS at all.

This is simply one advantage to using a real hardware raid card like the 3ware. There are plenty of other reasons too: Does your chipset/hardware support hot swapping? If you use SATA, does it support command queueing? Do your drives? How much cache does it have? Does it have cache? Can it tolerate all types of hardware failure? Does it have *ahem* 16 ports with individual controllers for each drive? It's not like the BIOS/IDE chipset makers write out in their specs how their hardware performs under drive failure conditions so you have the overhead of testing each configuration to make sure it works proeprly before you have to rely on it. It's not so much a performance difference between hardware and software raid (until RAID-5 anyway) but an issue with how the hardware will respond when something goes wrong, which is one of the primary reasons for using anything above RAID-0 anyway.

Yes, running a 3ware card costs more. There are times when that $400 costs a lot less than the time spent configuring and testing an alternative software-only implementation. There are times when it doesn't and spending another $400 doesn't make a lot of sense. I have run both setups. I have machines deployed with both IDE software-only RAID arrays, IDE 3ware arrays, SCSI software RAID5's, SCSI Adaptec RAID's etc.. it's all application specific. There's no reason to call somebody a goon for recommending 3ware hardware. It's really good hardware; maybe you should try it sometime.