Software RAID ever worth it?

[b0redom]

I had an OpenFiler install with 2 RAID-5 arrays one of them had a flaky disk which would sometimes not spin up on bootup. Openfiler would kick it out and renumber all of the other disks, so that:

/dev/sda
/dev/sdb
/dev/sdc
/dev/sdd

Would change to:

/dev/sda
/dev/sdb (was /dev/sdc)
/dev/sdc (was /dev/sdd)

This caused no end of headaches, as when the ropey disk appears again, it appears at the end (ie in the above case /dev/sdd having moved from /dev/sdb).

It appears that OpenSolaris, Nexenta, Ubuntu, Openfiler and FreeNAS all do this.

I don't really want to spend a couple of hundred on a hardware RAID-5 controller, as:

1) That's overkill for home use
2) It's expensive
3) If the card dies, I'm stuck with trying to find another identical card to try and get my RAID online

I'm currently toying with the idea of just scrapping RAID all together, having a bunch of disks, and non-destructively rsyncing important files between them.

Am I missing something fundamental about software RAID?

Cheers...

b0redom

[b0redom]

That should read RAID rather than RIAD, please can a mod fix?

[synaesthesia]

Other than it shouldn't be used on critical systems - it should be fine. But in general it's going to be pants compared to even a semi-decent controller. I replaced my software (mainboard driven) raid with a Perc 6i recently for just this purpose and it works wonders for speed.

Anyway, more specifically pertaining to your issue - would it perhaps be worth looking at the ZFS system? Still obviously software driven but being partially a file system and partially an LVM, it'll give you the same benefits of RAID for performance/redundancy/failover and I suspect it might be less susceptible to drive re-jigging.

[alsenior]

zfs is a good option it workes at the drive level rather than at the dev level. also it benefits from faster writes than raid 5. but dont look away from proper raid controllers. perc 5's and perc6's are as common as muck and will continue to be for years also dirt cheap as well

[b0redom]

My experience of ZFS is limited to Solaris on SPARC. It worked well, but Solaris provides real paths to the disks, so you can see what failed, and replace it easily. I'm not so sure how it'd work on an Intel based system - FreeNAS seems to label the disks as hdisk1, hdisk2, hdisk3 regardless of the controller/port they're plugged into.

@synaesthesia - Please can you provide a link to the Perc 5/6 card you're talking about?

If it can:

1) Alert me when a disk fails and identify it
2) Allow me to swap out the disk (I have hotswap HDD bays)
3) Rebuild the array with no further intervention

It might be worth considering. Data integrity is a bit more important than a few quid.

I realise that this is not a proper substitute for proper backups. All critical data is rsynced offsite to Amazon.

[ash_rm]

I've never had any issues myself with linux software raid. I've used RAID10 & RAID5 with it and always had really good performance. It can't be compared to windows software raid or fake raid.

But I agree the Dell Perc cards are worth a look since they can be picked up pretty cheap. Hardware RAID does saves a lot of hassle with it being OS independent.

Checkout this post on overclocker.net for some good info on the Perc 5 & 6 cards - http://www.overclock.net/raid-contro...card-tips.html

[alsenior]

iirc solaris x86 sees disks like this

c1d1t0
c1t1t1

or something like that. iirc correctly it the same way solaris on sparc does.

[synaesthesia]

I picked mine up for nothing due to my work (reuse,reduce, recycle!) however you can pick them up for £100 if you're lucky on eBay. I've seen them go for a lot less when they're sold by people who don't have a clue what they are, goofbay will come in damned handy. Otherwise I'll agree, they're not cheap :/