New Webserver with multiple drives

Mon Jul 28 08:36:32 PDT 2003

Matthew,

That explains it perfectly!  However, let me throw this on the pile and let me have your opinion on it:

1) Hardware load balancing is an option (or so I found out from the people that built the server) .. Using ATA133 RAID.  Being this is an option, should I hardware LB or software LB?

2) Personally, I like the idea of having 400gbs available.  This server is a web / database / email / dns server.  However, I'm desperately trying to see this in a more advanced light than "WOW, 400 gigs! WOOHOO!" :)  That being said, is Raid 1 the best way to go?  If it slows down writes, will it be noticeable?  The one thing I DON'T want is noticeable speed lost.  Is the Raid becoming corrupt in Raid 0 a common thing? I generally don't add to servers, I buy new ones.. So when I outgrow this production machine, it will get demoted to something else and I'll buy a bigger better production server. (meaning the chances of me adding additional harddisks is unlikely)

3) Does it matter that I'm planning an offsite location?  Essentially, I'll backup all the web / email / db stuff to a server offsite.  Although my backup server isn't as big as my production server (right now), I don't have 400 gigs of crap. I figure when I've outgrown my backup server, I can simply replace it.

Many thanks for all your help.. It's greatly appreciated!

Best Regards,
Duane

*****
Duane A. Stark
Drastic Productions, LLC
duane at thinkdp.com

> ------------Original Message-------------
> From: Matthew Seaman <m.seaman at infracaninophile.co.uk>
> To: Duane Stark <duane at drasticproductions.com>
> Cc: freebsd-questions at freebsd.org
> Date: Mon, Jul-28-2003 3:22 AM
> Subject: Re: New Webserver with multiple drives
> 
> On Sun, Jul 27, 2003 at 06:20:27PM -0500, Duane Stark wrote:
> 
> > To preface this, I'm not OS retarded - just BSD retarded ;)  I haven't had to mess with my current BSD server since I bought it, and now I have purchased a new p4 3.0(something), 2 gig ram, 2 IDE 200gig HD's to replace it..
> > 
> > Here is my question:
> > 
> > How do I setup these multiple drives?  What does the "industry" recommend when it comes to setting them up?  Should I set BSD up to think its one datasource (so 400gig) and then run from that? Or do I setup 1 drive to hold my web/mail/mysql, and the other to do something elsE?
> > 
> > I'm totally lost, so any help would be greatly appericated.. PLEASE don't assume I know what your talking about, because it's a given that I dont! heh :)
> 
> The only possible answer is "it depends".  With disks there are 3
> characteristics that you can modify the balance between depending on
> your needs.  Those are resilience, available space and access speed.
> There's also a fourth consideration, which may affect your choice but
> that has little effect during the day-to-day operation of the system,
> which is the amount of time and effort you're prepared to put into
> doing sys-adminly things.
> 
> Now, you've only got two disks, so that immediately rules out any
> choices involving RAID5.  You make no mention of any sort of hardware
> raid controller, so I'll assume that isn't a possibility either.
> 
> That leaves essentially 3 choices:
> 
>    i) No RAID at all.  This scores highly on the ease of admin, as
>       it's the default way things are set up by sysinstall.  Just
>       partition the disks, put filesystems on them and set up
>       /etc/fstab so the partitions get mounted in appropriate
>       locations.  I'll take this as the baseline to compare the other
>       setups to.
> 
>   ii) RAID 0 or disk striping.  This creates one synthetic 400Gb
>       partition from your two actual drives, by writing alternate
>       blocks of data to each drive.  The block size is configurable:
>       at one extreme you could make the block size the same as the raw
>       disk size, in which case you'ld end up appending one disk to the
>       end of the other.  However, the greatest advantage occurs when
>       the block size is round about the same size as the system can
>       read from the drive in one gulp.  This spreads the load of any
>       IO evenly of the two drives and should maximize performance.
> 
>       The bad news is that if either of the disks becomes faulty, then
>       all of the disk space on your system will be unavailable.  As
>       you add disks to the stripe, this problem becomes more and more
>       acute, so this setup is generally not used very much unless in
>       combination with RAID 5 or RAID 1 to give higher resilience.
> 
>  iii) RAID 1 or mirroring.  Each drive contains a complete copy of all
>       of the data, maintained in parallel.  The advantages are
>       improved resilience -- the system should just keep chugging
>       along merrily even if one of the drives self destructs -- and
>       improved IO performance on reads -- writes have to go to both
>       drives, which takes only slightly longer than writing to a
>       single drive, but reads can go to either drive which gives you
>       much better performance.  (The biggest factor is the
>       milliseconds it takes to position the head and wait for the
>       drive to turn round until the correct block is under the head.
>       Talking between the CPU, RAM and the disk electronics takes of
>       the order of microseconds.)
> 
>       The bad news is that you've got to sacrifice half of your
>       potentially available disk capacity.  However, assuming that the
>       resulting space is adequate for your needs, a mirrored root disk
>       setup is pretty standard for server machines.
> 
> Either of ii) and iii) will probably entail your learning about
> vinum(8) as the best available mechanism for doing software RAID on
> FreeBSD.  The alternatives are not that hot: ccd(4) is pretty ancient
> and doesn't offer any means of recovering a mirrored partition than
> backup and re-install should one drive fail.  I've heard that NetBSD's
> raidframe stuff is being ported to FreeBSD, but I don't think it's
> ready for primetime use yet.
> 
> See
> http://www.freebsd.org/doc/en_US.ISO8859-1/articles/vinum/index.html
> for a thorough introduction to vinum bootstrapping,
> http://www.vinumvm.org/ for general information and
> http://org.netbase.org/vinum-mirrored.html for a quick HOWTO set up a
> bootable vinum root drive.
> 
> 	Cheers,
> 
> 	Matthew	
> 
> -- 
> Dr Matthew J Seaman MA, D.Phil.                       26 The Paddocks
>                                                       Savill Way
> PGP: http://www.infracaninophile.co.uk/pgpkey         Marlow
> Tel: +44 1628 476614                                  Bucks., SL7 1TH UK
> 