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Would you suggest the use of a softraid-1 ???
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Would you suggest the use of a softraid-1 ???
No, it makes no sense at all
25%
 25%  [ 4 ]
Yes, but only for use in a server
31%
 31%  [ 5 ]
Yes, I use it for everything to feel save
43%
 43%  [ 7 ]
Total Votes : 16

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Master One
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PostPosted: Fri Oct 29, 2004 1:44 pm    Post subject: Would you suggest the use of a softraid-1 ??? Reply with quote

Until now, I always was in the opinion, I am on the save side, when using a softraid-1 on a machine, which is intended to be a lowbudget-server, because if one of the two drives should fail, the system is still operational.

But yesterday I ran into an issue, that made me think about it again, because on one of my machines a filesystem-error occured, leaving 3 file-entries in /bin, that I have no permission to as root. Only way to fix it, would be to boot from a livecd, and fix the problem with "fsck.reiserfs --fix-fixable", but that machine has no keyboard & monitor attached,and even does not have a floppy or cdrom-drive. So it's not a quick and easy fix.

A softraid-1 does not help at all, when a filesystem-error occures, and in my opinion, the chance for a filesystem-error is much higher, than a harddisk-hardware-failure (I never had one, also with very old and cheap IDE harddrives, that are in use 24/7 for years).

So my new point of view is now: Forget softraid-1! It's of no real use, and just eats CPU resources and a lot of diskspace.

What's your opinion?
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Petyr
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PostPosted: Fri Oct 29, 2004 5:30 pm    Post subject: Reply with quote

I'd still use it in a server but here's why. You're completely right that it doens't protect against a FS error, but it does protect against a HD crash. Usually raid is a part of a backup scheme. Not the whole thing, so in your case, perhaps you should consider something like bacula for doing your daily backups.
There's one other problem with soft-raid. If the primary HD dies on you, then your bios needs to be told to boot from the other drive. In addition, grub needs to be on the other drive as well! Otherwise you're kinda up sh**'s creek with a turd for a paddle.
The VERY nice thing about soft raid is that if you take those percautions into mind, and a drive dies on you, getting back up and running completely is pretty quick (certainly quicker than having to do a bare metal recovery!)

That's my .02 ^_~

Petyr Rahl
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JanErik
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PostPosted: Fri Oct 29, 2004 5:52 pm    Post subject: Reply with quote

Will the system keep running if a drive dies with IDE systems and software RAID?
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Petyr
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PostPosted: Fri Oct 29, 2004 6:07 pm    Post subject: Reply with quote

As far as I'm aware, yes it should continue to run, but I've not directly tested this per say (i.e. yank power on a drive that's live)

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Petyr
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JanErik
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PostPosted: Fri Oct 29, 2004 8:37 pm    Post subject: Reply with quote

OK, I was just thinking, it maybe depends on how it crasches... will it survive if the IDE interface does something strange - test pulling out the IDE cable instead.
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Master One
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PostPosted: Sat Oct 30, 2004 5:10 pm    Post subject: Reply with quote

As it's the only logical way, to put only one drive on each IDE channel, it would be absolutely no problem, if one disk dies in a softraid.

The major problem is, having a decent filesystem on a softraid-1, which can produce filesystem errors without the usual influence from outside, because access to a softraid causes the double stress to the CPU. AFAIK XFS even does not perform at all on a softraid-1 (can't remember the reasons, but I think it has something to do with nodes or chunksize).

I have ReiserFS-3.6 on that softraid-1, which consists of two IBM UltraStar 18.2 GB U160 harddrives on oen Adaptec 19160 controller. The system was rock stable and was running 24/7 until now for a longer time. It was not a power-failure (e.g. a condition with an unclean unmounting), that caused that filesystem-error. It just happened during an emerge. There is no logical explaination, how such a thing can ever happen.

I am still unsure, if I should keep it as softraid-1, or go back to two single drives. It would give that machine (it's only a Duron 1300) a noticeable performance boost (less stress on the CPU, and faster access with moving heavily used partitions, like /var and /home, to the second drive). I think the chances for a filesystem-failure are less with single drives, the only downside is the missing safety when thinking of a drive-failure.
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PostPosted: Thu Dec 23, 2004 10:06 pm    Post subject: Reply with quote

Well, actually error resistant RAID (like 1 or 5) does only help in specific circumstances, but in my opinion, those are the most important ones.

You're right - if the filesystem gets corrupted, no RAID will ever help you. It's either a means to extend (and/or speed up) your filesystem or to provide some protection against hardware faults.

You have to rely on your chosen filesystem to be stable (I personally never really had troubles with neither ext2, ext3, reiser3, nor xfs - which I haven't been using for very long, though - during the last 15 years). But from my experience, yes, shit does happen, but far more often it's the harddrive failing mechanically or electrically. And that's where a RAID really shines.

I run Gentoo on some HP ProLiant servers with hardware RAID at work (cciss driver fo 5i and 6i controllers) which is really great, but I also use the md software RAID which is okay for non-professional use at home.

If you can spare the money (decent harddrives are quite cheap these days) and have any valuable data (most of us have, I think), md RAID is a nice thing to have in, my opinion.
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