On Apr 26, 2011, at 12:08 PM, Les Mikesell wrote:

> 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.
> 
> But, note that even though you don't technically have to stop/unmount 
> the raid while doing the sync, realistically it doesn't perform well 
> enough to do backups at the same time. I use a cron job to start the 
> sync very early in the morning so it will complete before backups would 
> start.
> 
> -- 
>   Les Mikesell
>     lesmikesell AT gmail DOT com

All my sata drives are "external" internals. That is, they are connected to PCI 
sata controller but since there are no bays to install them in the computer 
chasis, I just run the cables outside through a PCI slot bar. Still have to 
figure out the a long-term housing solution. At least they are easy to access.

So I would be ok doing something like this:
Stop BPC process
Unmount raid array (md0 made up of sda1 and sdb1)
Use mdadm to remove sdb1 from the array
Take off the sdb drive, attach offsite one in its place
Use mdadm to add sdb1 to md0 and reconstruct

Maybe cycle through whether I remove sda or sdb so all drives get used about 
the same amount over time.

My main concerns were: can I remount and use md0 while it is rebuilding and 
that there is no danger of the array rebuilding to the state of the newly 
attached drive (I'm very paranoid). I assume that as long as I use mdadm to 
remove and add sdb, it will use sda as the base (or vice versa).

Mike




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