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Experiences w/ Software RAID 5 Under Linux?
MagnusDredd asks: "I am trying to build a large home drive array on the cheap. I have 8 Maxtor 250G Hard Drives that I got at Fry's Electronics for $120 apiece. I have an old 500Mhz machine that I can re-purpose to sit in the corner and serve files. I plan on running Slackware on the machine, there will be no X11, or much other than SMB, NFS, etc. I have worked with hardware arrays, but have no experience with software RAIDs. Since I am about to trust a bunch of files to this array (not only mine but I'm storing files for friends as well), I am concerned with reliability. How stable is the current RAID 5 support in Linux? How hard is it to rebuild an array? How well does the hot spare work? Will it rebuild using the spare automatically if it detects a drive has failed?"
Actually, a big disadvantage to hardware RAID is what happens if your controller fails.
Consider--your ATA RAID controller dies three years down the road. What if the manufacturer no longer makes it?
Suddenly, you've got nearly 2 TB of data that is completely unreadable by normal controllers, and you can't replace the broken one! Oops!
Software RAID under Linux provides a distinct advantage, because it will always work with regular off-the-shelf hardware. A dead ATA controller can be replaced with any other ATA controller, or the drives can be taken out entirely and put in ANY other computer.
Is there a good resource for hardware/software RAID support on linux? Tech support is always a challenge and we have a number of 3ware 8way and 12way powered by 250gb drives. We often have lots of mysterious drops on the array that require reboots or even rebuilding the array. Royal pain in the ass.
Laboratree - Scientific collaboration based on OpenSocial.
This is the worst possible type of advice. Do you have any reason for not using them? Maybe you've bought dozens and they've all blown up and burnt your house down, which would be a good reason to not buy 3Ware. Maybe you work for a competitor.
For all I know, you could have a very good reason. But if you tell someone to make sure to to stay away from something, you should provide a reason. Especially if it's something that seems to have a really good reputation.
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suwain_2
The cheap raid controllers are almost always software raid and not worth it. If performance is critical some of the higher end SATA and SCSI raid stuff is worth it, but a lot of that sucks too so do benches, take recommendations and don't believe in brand names...
Don't hang a pair of drives off each controller. Get a truckload of PCI ATA cards or a card with multiple controllers. Don't slave a drive. (No, I do NOT know what the correct PC term is for this).
Also, give 'mdadm' a whirl - a little nicer to use than the legacy raidtools-1.x (Neil's stuff really rocks!)
Software RAID5 has been working extrememly well for us, but it is NOT a replacement for a real backup strategy.
one better than mcleodeight
Hi,
:
The scenario you've mentioned is probably OK to use a software RAID. I use it in a production enviroment without problem with a higher stress that your setup will probably have.
I'd suggest you to consider the following items
a) cooling system - those HD can generate a lot of heat. Buy a full tower case and add those HD coolers to make sure your HDs stay cool
b) Buy the HDs from different brands and stores - RAID5 (either hardware or software) can recover from one drive. If you buy all from the same brand/store chances are that you end up with 2+ drives with the same defective hardware
c) cpu - if you are going to use this number of drives the processor will be a majo bottleneck. Do not forget that RAID5 XOR your data to calculate the parity.
d) partition scheme - use smaller partitions and group them together using LVM. This you help you to recover from a smaller problem without taking a lot of time to reebuild the array