Looking For RAID Hardware/Software Advice

[Craig White]

On Fri, 2009-01-16 at 09:36 -0700, Mark Phillips wrote:
> I am running out of room for my backups. I use backuppc and I have
> almost filled a 150GB drive with backups from 7 computers, and I need
> to add another 2 computers to the set. I have an old Dell Poweredge
> 1300 server (Pentium III 550 Mhz, 500 MB RAM, PCI 33.3Mhz) that I
> could turn into a backup server. I am looking for suggestions/thoughts
> on how to set this up. I need to keep the cost down as much as
> possible; under $150. 
> 
> My initial thoughts:
> 
> * Keep current 72 GB drive for OS (debian testing, about 68% full)
> * Add two 500 GB SATA drives and a PCI SATA controller ~$130
> * Software RAID and LVM for the two drives
> * Move current 150 GB of backups to the RAID
> * Backuppc now runs on this machine and slowly fills up the RAID
> 
> 
> My questions:
> 
> 1. Should I keep the 72 GB drive for OS, or put it on the RAID?
> 
> 2. I can add another CPU (P III 550 MHz) processor to the box - is it
> worth the effort to find one? I found one source for $5/CPU, I just
> need to find the heat sink and mounting hardware. Will this improve
> performance?
> 
> 3. The box has a built-in SCSI 68-pin Ultra2/wide bus/controller, but
> SCSI drives are more expensive, at least from a cursory google search.
> Is this correct? I don't think I can use SCSI drives within my budget
> constraint.
> 
> 
> 4. Would upgrading the memory to 1GB improve performance - top shows:
> Mem: 646676k total,      639300k used     7376k free,      64548k
> buffers
> This would add another ~$60 to my cost.
> 
> 
> 5. Should I look at hardware RAID cards - they seem very cheap, so
> perhaps software is better?
> 
> 4. Does this plan make sense, or is there a better way to proceed for
> about the same cost?
----
1. One of the tricky things about backuppc (and I don't use it so I am
working from just a general understanding of things) is that it
creates/utilizes lots of hard linked files so if the boot os dies, your
backup may die along with it. The point of RAID is the redundancy part
which means things just keep working even if there's a complete failure
of a single hard drive (assuming everything but RAID 0). Having a RAID
array for your OS would ensure that.

2. Real hard to match processors at this point and unlikely you would
find one that exactly matched. Might be easier to find 2 that match each
other and install them both but for a backup box, that seems
unnecessary.

3. Yes, SCSI drives are more expensive - but performance should be much
better.

4. RAM may help a little. Free shows output of virtual memory but
doesn't suggest how much real RAM you have there. Assuming a text based
interface (not GUI), 256 MB RAM for what you're doing should be enough.

5. Cheap RAID hardware cards are cheap because they suck. Most of the
SATA 'RAID' cards are either 'fake' RAID (they aren't really hardware
RAID) and perform especially poorly on commonly used RAID 5 (3 drives
minimum but maximum drive space).

6. Makes sense.

Software RAID works well. You can create a RAID volume for your OS is
you wish - i.e. one drive on SCSI and one on SATA but the suck thing is
that...
- You can't just convert from an existing filesystem to a RAID array.
You'd have to copy it all off, create your RAID array, copy the files
back and then fix the boot issues
- RAID works much better if the drives are on different controllers - a
controller can only write one drive at a time.

Craig