[lists] Re: [NMLUG] More RAID Questions

[kwilson at swcp.com (Kelly Wilson)]

RAID5 scenario.

> 1. Someone noted that software raid was just as fast as hardware 
> raid.  This
> machine will be a mostly dedicated Samba Server on a P4 1.8ghz 
> machine.  Does
> this still hold true or should I get a dedicated Promise Controller that
> supports RAID5
>  

I would disagree with software RAID being faster than hardware RAID.
I manage around 70 production servers and ALL of them run hardware RAID 
with onboard cache. Regardless of how much or how little resources are 
consumed by software RAID, specialized hardware IS faster and with no 
effect on the OS. Rebuilding IS faster with hardware.

> 2. I thought I read somewhere that you should only use Drive0 on each
> controller when using with RAID or you will get horrible performance.  
> Does
> that hold water?  My onboard Promise RAID controller can be configured 
> for
> RAID or normal ATA100 IDE controllers.  As normal IDE controllers that 
> would give me 4 controllers with 2 drives each.  With the above 
> limitation it
> sounds like I would only be able to use the Drive0 on each controller 
> for my
> raid array.  Could I use Drive1 for occasionally used devices 
> (IDE-DVD/CDrom,
> Large Backup HD) without a performance hit?
>  

I've never heard anything about the Drive0 issue you mentioned. I do 
know that a couple of SuSE systems I have running SATA complain about 
the Promise and the FastTrack IDE raid controllers not working under 
Linux as "real" raid and advise against writing to both disks. You have 
to be careful and only mount and use the first drive of a pair. Look to 
spend a little bit more and get a better IDE RAID controller that is 
truly OS transparent. Adaptec and a few other vendor make such controllers.

> 3. What is the math for RAID5?  I really only need around 60 gigs of 
> storage.
>  


For a RAID 5 setup, try not to go more than about 6 or 7 drives to a 
raid set. You lose one drive to parity and the rest are all space. In a 
RAID 5 set, you'd need a minimum of (3) 30Gb drives to get a 60Gb 
partition. In RAID 1 ( better performance) , you'd need just (2) 60Gb 
drives to get the same. RAID 5 (decent performance) allows you to lose 
one drive and continue running albeit without any redundancy until the 
failed drive is replaced. RAID 1, you can also lose a drive (either one) 
and continue to run without problems but again without a failover until 
the failed drive is replaced. RAID parity overhead is higher on RAID 1 
but performance is higher. RAID 5 overhead is lower but also lower 
overall drive performance.

>
> 4. I'm looking at getting 3 40 gig ATA100 HD's for the raid array to 
> add to
> the existing small HD for the linux OS, a 200 GIG HD for a rolling couple
> days backup, and the IDE-CDrom drive.  How would you suggest hooking 
> all that
> up considering question #2?
>  

IDE controllers are typically two channels with two drives per channel 
for a total of 4 drives per IDE controller. One drive on each channel 
being master and one being a slave. If I was you, I'd really consider 
getting (2) 80Gb drives and doing RAID 1. You'll probably leave the 
small OS drive you mentioned on the primary onboard IDE controller as 
/dev/hda, the 200Gb drive as /dev/hdb, (your CDR/DVD drives on the 
second primary IDE channel as /dev/hdc and /dev/hdd. The onboard IDE 
RAID controllers generally appear as /dev/hde and /dev/hdf, (I have 3 
such systems, one with a FastTrack, one with a Promise, and one with a 
Silicon Image chipsets. ) As I mentioned, Linux doesn't seem to think 
very highly of those (they're deprecated in the 2.6 kernels..) and sees 
them as some sort of "software" raid. If you go ahead and run it this 
way, don't mount /dev/hdf directly, just mount /dev/hde (first of the 
two) and you should be fine.

> 5. Any tuning tips for Samba with WinXP workstations?
>  

You may have to tweak the registry in XP to do encrypted/unencrypted 
passwords. I have the O'Reilly samba book and I seem to remember 
something about that. I mostly support Windows 2000 clients. Also, 
windows users don't usually know what to do with dotfiles (.bashrc, 
.xinit, etc..) so you can hide those with options in smb.conf.


Hope it helps.

-- 
Kelly Wilson

 

>