On Oct 26, 2009, at 12:13 AM, Eric Shubert wrote:

> .) I don't know about hot-plugging drives. Since you're talking  
> about a
> backup server though, what's the big deal about hot swapping? Just  
> shut
> the thing down and swap the drives. What's the advantage to leaving  
> it on?

Well, mostly just the time involved.  I do think cold-swap is an  
option, but I'd rather be able to move the drives around without  
needing to shutdown & startup.

>
> .) I like the rsync/USB solution the best. rsync doesn't really take
> that long, even with USB (slow) connected drives. I have a backup  
> server
> running raid-1 on USB drives. The only real problem I had was that the
> raid array tried to start before the USB drives were completely  
> active.
> Added a "sleep 10" statement in the init script and it works fine. If
> you really need more speed, use eSATA with external drives instead of
> USB. Yes, eSATA and SATA are different.

I don't claim any expertise here, but afaik they are different in  
connector shape only.  I've seen several eSATA<->SATA converter cables  
which seem to support that theory.

Neither inherently provides hot-swap.  That's a feature of AHCI, which  
may or may not be present in a disk controller.  Having an eSATA port  
on a non-AHCI controller seems a little pointless, but I think it's  
possible from the research I've done.  I ordered an ASUS motherboard  
with an Intel ICH10R southbridge, which does support AHCI, as well as  
a pair of USB/eSATA external disk enclosures.  If I can get hot- 
swapping to work with eSATA, then hooray.  If not, I can fallback to  
using USB.

http://en.wikipedia.org/wiki/Advanced_Host_Controller_Interface

I decided against making the 3rd drive part of the RAID array for a  
few reasons.  First, the disk activity required to rebuild a RAID is  
probably more than that required to rsync files, so going the RAID  
route means more wear & tear on the disks.  Second, having the 3rd  
drive separate from the main disk array means it's that much further  
separated in case of some error.  The 3rd drive can be umounted 90% of  
the time, and only mounted when a new backup job runs.

I liked the idea of keeping the server chassis tidier by having the  
swappable drive mounted internally, but thinking about moving bare  
drives from place to place on a weekly basis got me thinking about  
damage, static, etc.  Also, an internal drive is going to have the  
same power supply as the main drives, which adds another avenue for  
all 3 drives to suffer the same fate simultaneously.  All in all, an  
external drive made more sense, even if the neat-freak in me doesn't  
like having to keep the extra box piled on top of the server.

alex