On 07/23 12:50 , Les Mikesell wrote:
> I've never seen anything go wrong with Linux RAID1 over 6 or so years 
> and dozens of machines and I've abused it with things like hot swapping 
> SCA drives and rebuilding the replacement, cloning machines by splitting 
> the pair and letting both rebuild a new mirror, and using a 3-member set 
> with one normally missing for my backuppc archive.  What kind of 
> problems have you seen?

- When one drive dies, the whole machine kernel panicking and locking up.
  The data was still good on the second drive; but it required a site visit
  to get things working again; and then another site visit to replace the
  drive.

- One disk in an array sort-of kind-of dead, but still throwing bus errors
  and slowing things down. Then causing the whole machine to panic when the
  drive was poked with hdparm (new techician said "oh, it's running slow,
  I'll just hdparm -X69 it" and did so before I could stop him).

- First disk in an array dying, and the second one not being bootable.
  (You have to write boot records to the disks individually, and either
  someone typoed the command in this case, or GRUB failed to write what it
  should have, both of which are concievable).

- When building/rebuilding arrays it's *very* easy to transpose partition
  numbers or device names and wipe out all your data. (Remember that when
  this stuff goes wrong it's never at a good time; so you're stressed and
  sometimes tired). (yes, this is a user issue not a technology issue).

Those are just the issues that I personally have seen. None are
insurmountable; but they are tremendously inconvenient.

In our experience, 3ware controllers make the drive replacement process so
much easier 90% of the time, that they more than pay for themselves in
reduced labor costs when things go wrong. Software RAID is false economy in
a corporate environment where labor costs 50-100s of $/hr. 

I do appreciate your position tho; and the flexibility that software RAID
offers is needed in some applications.

BTW, LVM can do RAID0/RAID1 as well. Unfortunately they don't have any good
error messages that tell you when one partition in the array is not sync'ed
with the other (in the case of RAID1). This lost me a notable amount of data
(fortunately my own, not someone else's).

-- 
Carl Soderstrom
Systems Administrator
Real-Time Enterprises
www.real-time.com

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