Re: HW RAID configuration - best practise question(s)

[Jens Knoell <jens@surefoot.com>]

Good morning :)

Dermot Paikkos wrote:

>Hi admins,
>
>I'm about to buy a custom build server and wanted to know to 
>configure the RAID. This will be the first time I have configured a 
>RAID from scratch and I am a little un-sure about how the layout of 
>the system.
>
>The server will primarily be used as a file server, uses a 3Ware SATA 
>8 port card and will serve about 50 users. There will initially be 4-
>5 disks installed. I would like one as a hot-spare but it isn't 
>written in stone at this time.
>  
>
Well, for starters there are a bunch of different RAID options 
available. I'd go with RAID 5 if the controller supports it. To Linux 
it'll just appear as one physical disk anyway, i.e. you do not 
necessarily need to worry about any RAID config issues in Linux itself.

A hot-spare is nice to have, but IMO not immediately useful. I tend to 
keep a brand new (tested OK) disk on hand, but not plugged in. It all 
depends on how closely the system is monitored. In my experience it's 
rare that two disks fail immediately, and RAID 5 can work with one 
failed disk just fine for a limited time.

>My own thoughts were to keep the root file system outside of the 
>RAID.
>This would allow me to do a complete OS re-install without effecting 
>the RAID. There are a couple of reasons why an OS re-install might be 
>desirable: I may change my distro (currently slackware) and I may 
>choose to try the i64 instead of i386 (AMD Opteron). This is just my 
>thoughts and there may be some good reasons for not configuring the 
>system in this way. If you have any please let me know.
>  
>
Personally I wouldn't bother splitting one disk off the RAID array. You 
really don't gain anything, unless you have a good reason to run the 
disk in a non-RAID environment - i.e. if you preconfig the disk in 
another machine and then move it to the server or something.

>What about swap? How should you configure the swap space on such a 
>system. Can swap space be assigned to a RAIDed file system? Should 
>it? 
>  
>
Yep it most certainly can on hardware RAID. For performance reasons it 
should be on RAID too, IMO.

>Is there anything else I should be thinking about or any documents 
>should read (I tried tldp.org but nothing struck me). Any thoughts?
>Thanx.
>Dp.
>
The only thing you need to look for is the matching kernel module to 
boot from that controller. Other than that... nothing I can think of. I 
just slapped Slackware on an IBM e-Server with ServeRAID, and it worked 
perfectly on first try. I've simulated disk failures too... everything 
went rather smooth.

J.