On 4/27/11 12:44 AM, Jeffrey J. Kosowsky wrote:
> Les Mikesell wrote at about 12:08:22 -0500 on Tuesday, April 26, 2011:
>   >  On 4/26/2011 11:38 AM, Michael Conner wrote:
>   >  >  I installed BPC a few weeks ago and have been doing testing and setup 
> since then and have things working pretty well on several linux, windows, and 
> mac clients (ultimately there will be about 15 clients). The server is a Dell 
> 2400 with a 160gb ide drive, Centos 5.6, BPC 3.1 installed with yum from the 
> testing repos. I've added a sata controller and two 2t drives as a raid 1 
> setup, which is what I'll use for real backups. I can't boot off the sata 
> drives, so I boot from the ide drive and put topdir on the satas.
>   >  >
>   >  >  I've done some searching on offsite backups as I would like to 
> maintain at least a recent copy offsite as disaster protection. DD has been 
> too slow for these large drives (I would have to leave it going overnight 
> with no backups running). I may go with periodic archives using the BPC 
> archive function.
>   >  >
>   >  >  However, another idea intrigued me that I saw in an earlier posting. 
> Someone used a RAID 1 setup but only put in the second disk periodically, 
> then removed it for offsite storage. I have three 2T drives, so was 
> considering something similar where I would keep a normal 2-disk RAID 1 setup 
> but periodically remove one disk and replace it with a prior offsite disk.
>   >  >
>   >  >  Not being particularly experienced in all this, I was hoping someone 
> on the list could offer advice on whether this was a good ideal or not and 
> potential pitfalls.
>   >
>   >  It is working for me, but I use a 3-member RAID1 where 2 are always
>   >  connected and the 3rd is rotated out periodically.  This isn't really
>   >  necessary but when I was first trying it with one internal, one external
>   >  drive the internal one failed, corrupting the attached external, and it
>   >  was something of a hassle to rebuild from the remaining offsite external.
>
> I did it that way where the 3rd 'backup' drive was mounted via USB and
> had a *catastrophic* failure where something went wrong with the 3rd
> drive causing all three RAID1 members to become corrupted. I'm not sure
> exactly what but I ended up losing 2 years of backups.

I think that's similar to saying "lightning struck my house while using RAID so 
I'll never use it again".   It's actually very difficult to get mdadm to do 
something wrong even if you try since it warns you if you try to use partitions 
that are busy elsewhere or the wrong size.  I wouldn't recommend using USB in 
production though, and would guess the failure was more likely related to 
hardware/drivers than the software raid layer.   Firewire/esata are OK for 
external enclosures and swappable internal sata bays are even nicer.

> I think a safer alternative would be to do what the OP proposes --
> that way you always have one safe copy not part of the RAID in case
> something messes up....

You need that anyway, although starting from scratch it doesn't matter since 
you 
have nothing to lose.  When you were trying to convert an old 2-member set to 
3, 
you should have failed/removed one of the existing drives (at least logically) 
until you had added the first external and then rotated it offsite, after which 
you would always have the working spare.  There always is a danger that the 
current sync will hit an error on the source leaving the whole set unusable, 
although this should be greatly reduced when the source is a 2 member mirror.

-- 
   Les Mikesell
     lesmikesell AT gmail DOT com

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