[clug] forget RAID?

Michael Cohen michael.cohen at netspeed.com.au
Thu Feb 22 04:26:31 GMT 2007

On Thu, Feb 22, 2007 at 01:37:50PM +1100, David Tulloh wrote:
> never going to be able to achieve 100% reliability though.  I can't 
> really see how it would ever be better to tar and copy to another disk 
> compared to RAID, maybe if you wanted to keep multiple backup versions.

  RAID is not backup ... its always better to tar and copy to another disk than
  to rely on RAID. Put it simply - the data on the disk is vulnerable to a
  number of events - one of which is the disk dying. RAID aims to address this
  threat - but there are lots of other threats to your data, like user error,
  file system corruption, deleting files, overwriting files, getting hacked
  etc, etc, etc...

  None of these scenarios are addressed by RAID at all.

  You should have both RAID and backups. RAID is useful to address the issue
  when a disk dies, and it enables you to keep working without taking the
  system offline - thats important for some applications. If one of the other
  events occur - you will have to consult your backup regime and you may or may
  not have downtime. You may well decide that your data is totally unimprotant
  and you can live with the effects of the other scenarios - and thats fine,
  depending on how likely you think they are to occur.

> Personally I use RAID to ensure that I don't permanently lose data.  
> When I get a drive failure I simply shut the whole thing down until I 
> get another drive, I don't really mind if it's not accessible for a day 
> or two so long as it doesn't all permanently die on me.  I think that 
> most companies which are seriously worried use multiple disk suppliers 
> (I have two brands in my three disk array) and multiple redundant drives.

  What you describe is a compromise which doesnt really make the best of RAID -
  you dont mind having downtime as long as you dont lose data. RAIDs best
  feature is little or no downtime but there is little guarantee on data
  integrity. Maybe backups are better for you?

  I find that monitoring smart really helps to let you know when a disk is
  about to die, which helps you plan for replacing it.


> David
> Tomasz Ciolek wrote:
> >Hi Guys
> >
> >Actually I checked up on this when dping some research a few years
> >sgo... 
> >
> >and I am told by people in EMC, who deal with storage for living, 
> >that they deliberately mix batches of disks into a single stock 
> >pile before installing disks...
> >
> >I epxect most GOOD rais suppliers do that too. 
> >
> >In my experience temperature and a dodgy power supply is more likely to be 
> >a cause of disk death, than batch issues.
> >
> >Cheers
> >Tomasz
> >
> >  
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