Painless Linux Raid?

[dnoyeb]

Once again after about 1-2 years good work my Linux box is getting flakey. I want to probably get a new MB but im thinking just to get a RAID card. The only thing that ever seems to fail is either a harddrive or the harddrive controller on the MB.

So my question is should I just get Hardware RAID? It seems that the software RAID may be RAID but it does not offer the painless replacement of the drive. First both drives are not in a full RAID, only certain partitions are. Which does not really include the boot partition. So if the boot drive fails, im SOL and I gotta figure out how to boot my computer. Then I gotta remake the boot partition somehow before I can even consider rebuilding the array. Plus I would have to repartition the new drive so I gotta remember the partition.

It just seems like while software RAID works, if one of the drives dies I have to deal with some serious PAIN which for me I just don't want to do.

I am using REdhat 9 right now, so if its different, or you can give me tips or point me into a more painless direction, please do! I am considering hardware RAID, but don't know if this will make any difference.

Thanks for your tips!

p.s. its my personal computer which holds my email, software i wrote, old papers, etc. stuff I don't want to loose. I still backup about 1/month to CDROM...

 

[drag]

Unless your willing to spend 300-400 dollars on a good RAID card, forget it.

Cheapos (30-100+ dollars) are more apropriately called 'BIOS' raid. They are like Winmodems were they have very very limited hardware support for RAID and most of it is done in software and franky Linux software RAID is superior in performance, capabilities, recovery abilities, and stability. Compared to Software RAID, the 'BIOS' cheapo RAID cards are a huge pain.

If you want performance, buy a faster drive. RAID isn't going to get much higher performance unless you have lots of drives. Especially during writes the cost of keeping parity and mirrors of information incures significant overhead. I have a 3 disk software RAID 5 setup and performance is sometimes slightly above a single drive (for reads generally) and sometimes slightly lower then a drive (for writes mostly). Mirrored RAID 0/1 are the same. The overhead of maintaining the RAID array kills most of the performance benifits. Mostly of what people see when using striped raid is a placebo.

If you doing it for reliability.. this is good. It will gaurd against mechanical failure of your drives and it is fairly easy to rebuild a array (but the proccess can take a few hours). However it will not help against electrical problems (power surges, power failures, etc) and will not do much to prevent file corruption. (if you have a drive that is failing and causing data corruption, that data corruption has a good chance of ending up mirrored as actual data on the other drivers before it fails completely).

So raid is good for reliability and uptime and can possibly be good for performance, but is not a substitute for backups.

Another angle you could look at, I suppose, is getting a external housing for a harddrive. Something that it makes it easy to do quick backups inbetween cd backups. Like a firewire or a USB 2.0 housing. You copy over a image of your system and your home files, it gives you some extra room if you need to move something around, and it can be kept connected for use or disconnected to avoid any power surges and such.

Also a UPS is nice.

Most of the time it's fairly easy to setup Linux RAID , most installers support that option. I know Debian 'Sarge' does for a fact, and I am pretty sure that Fedora and such would.

Also on top of that (or on a plain drive) I have grown fond of LVM, which makes managing disk space much easier. It allows you to setup 'virtual partitions' and resize them and move them around and such. And you could add volumes to them and expand them to make more space for files and such. There is some overhead to it, but it's not that bad.

For recovering your 'boot' partition it's not that hard to use a Linux rescue disk like Knoppix or one that is supplied by Fedora Core installers to manually go in and use 'chroot' to gain access to your system and reinstall the boot loader manually. Chroot command allows you to 'change roots', that is to switch your enviroment from one root directory system to another.

Of course LVM and RAID add complications and makes it more difficult to recover sometimes vs a straight traditional partition setup. So like everything it's a trade off. The simpliest solution seems to me to have a seperate harddrive in a external enclosure or disconnected in your computer that you plug in time to time to help move files around and provide a extra level of backup-ness.

For more information...
Linux SATA Raid FAQ:
http://linux.yyz.us/sata/faq-sata-raid.html
SATA status report information:
http://linux.yyz.us/sata/
Software RAID howto:
http://unthought.net/Software-RAID.HOWTO/Software-RAID.HOWTO.html
LVM howto:
http://www.tldp.org/HOWTO/LVM-HOWTO/

 

[dnoyeb]

Speed is absolutely NOT a concern. Ease of rebuilding the array is. as well as ease of installing.


I am willing to spend 300-400 dollars to buy reliability and ease of use. If this means

1. when if fails I simply pop in a different drive and push rebuild.
2. If one drive failes I dont have to worry if the boot sector was on that drive because /boot is also RAIDed.

Drives are so reliable that by the time they or the MB fail I forget how to install Linux, and have no idea how to 'reinstall' the boot sector, nor how to repartition the new drive to match the old one. Things I think HW RAID means I dont have to worry about!?

Currently I have a 3rd drive that has my music on it that I dont backup. It also has the backup partition on it that I backup a CD image of the important parts of my main drives to once every 2 weeks or so. Then once a month I actually burn it to CDROM.

Ease of use is what I am after.