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Re: hard- or software-raid?


On Fri, Jan 24, 2003 at 10:26:43AM +0100, Tinus Nijmeijers wrote:
> My question kind'a stands: If the only thing I ask of it is for the data
> to be safe (no speed or "no downtime!" issues) is there any reason to
> use hardware over software raid?
> I do not care if I have to take the server down for an hour (or 2, or 3)
> to replace a disk, be it a raid disk or boot disk. I have plenty of
> time, I could even run down to the store, get a new bootdisk, install
> debian and be up and running in 2 hours. no problem. 
> ONLY thing that is important is that the data needs to be safe. if 2 of
> the raid-disks fail I need the data to be safe.

I'll say that raid is not the thing you want. Maybe to make a big
partition but not for safe data. What you need is a backup system.

The reason is that raid can only handle hardware failures. Software
failure and/or user/admin mistakes kan not be handled this way.

When a file is deleted it is gone.

> (it is, of course, a budget thing. In case of fire I have tapes to get
> the data back, there's downtime involved there. So I do care about
> downtime. Just that with disks being as cheap as they are I was thinking
> that a software raid is soooo cheap to build that maybe that's worth the
> extra cash for the 3 extra disks that I need to buy.

Now I do not really understand. You have tapes and you still want
raid because there is downtime involved and you do not care about downtime.
I do not trust tapes but that is another issue.

> scenario 1: boot of scsi, data is on a 200G IDE, tape backup
> scenario 2: boot of scsi, data on 4x80G IDE (software-raid5), tape
> backup  = + EURO 100
> scenario 3: boot of scsi, data on 4x80G IDE (hardware-raid5), tape
> backup = + EURO 500
> scenario 4: boot of scsi, data on 4x80G SCSI (hardware-raid5), tape
> backup = + EURO 2200

You have thought about hard-disc backup instead of tapes. But I assume
that you already have a tape solution so that it is out of budget.

> so for close to nothing (E 100) extra I get software raid.
> Is hardware raid "safer"?

Yes and no.

If the raid controller fails (you will probably only have one) you can
have serious problems.

On the other hand hardware raid is easier (less admin errors) and also
can detect hardware failures earlier.

> (I do not think it is, I'm just waiting for someone to tell me I'm being
> naive here)


// Ola

> Tinus.
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 --------------------- Ola Lundqvist ---------------------------
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