[BBLISA] Fwd: Re: Fileserver opinion

[Daniel Feenberg]

On Mon, 30 Aug 2010, John Stoffel wrote:

>>>>>> "Daniel" == Daniel Feenberg <feenberg at nber.org> writes:
>
>
> Daniel> A simple Linux or FreeBSD box with 12 2TB drives can be
> Daniel> assembled for $3,000. I wouldn't put a RAID 5 on it (because
> Daniel> Linux and FreeBSD don't do a good job of reconstruction after
> Daniel> a drive failure - see
> Daniel> http://www.nber.org/sys-admin/linux-nas-raid.html ) but a RAID
> Daniel> 1 will provide reliable, but not fast storage. Suppose that
> Daniel> the formatted storage capacity is a third the total drive
> Daniel> capacity - that makes the cost about $375 per TB.
>
> So what happens when two disks fail?  How do you get notified and can
> you rebuild your parity/redundancy without *any* downtime or even real
> notice by your users?

Well, different groups have different requirements. The OP may be able to 
withstand some downtime, there is no need for this group to brand him as 
unprofessional for taking that point of view if his employer agrees. The 
FreeBSD or Linux Raid will require downtime for drive failures, and in my 
experience a rebuild is probably not possible - the files will need to be 
copied afresh from the surving drive onto a new partition. The reason for 
this is that the rebuild will stop on any read error on the good drive, 
and a good drive is likely to have a bad sector on an unwritten portion of 
the drive. The rebuild covers the entire drive, not just the portion with 
files. So the files are all available, but a rebuild is not possible. 
This is a disadvantage, but not a loss of data and needs to be balanced 
against cost considerations.

>
> I only ask because this is a hard thing to get right, and takes time
> and effort to test properly.  90% of all scripting and coding seems to
> be bounds and errror checking, not to mention check pointing state and
> rolling back or committing changes when you know you can.  Computers

Is it a bit odd that the indication of a failed drive is so subtle. Has 
anyone seen a package to do surveilance and notification for RAID groups 
on FOSS operating systems?

Daniel Feenberg