[COLUG] SATA RAID controllers for Linux

[Brian McDonald]

On Friday 20 June 2008 9:06 am, Joshua Kramer wrote:
> 
> > Let me rephrase, I can effectively buy twice as much hardware now, as a
> > single server + hardware raid solution, I also find throwing as much ram
> > as possible at servers tends to alleviate a lot of DB IO wait issues
> > when you properly tune the database.
> 
> What about the other esoteric features of HW raid, like hot swap and auto 
> rebuild?  If I have 6 SATA drives in hot-pluggable carriers, and one of 
> the drives goes south under a Linux Software Raid configuration, is the 
> kernel 'smart' enough to allow me to just yank the drive, and start 
> rebuilding it when I plug in a new one?  Or do I have to take the server 
> down for this rebuild to take place?

Hot-swap is a function of your mounting hardware and of your OS.  Recent Linux 
kernels handle hot-swapped SATA.  Even older ones are okay with hot-swapped 
SCSI.  I don't have extensive experience with the varoius RAID techs on 
linux, but all the other software RAIDs I've worked with (vinum, geom on BSD) 
supported the idea of hot spares at least, and setting up an automatic 
rebuild wouldn't be extraordinarily difficult.

It's like Duane said - there are a whole bunch of applications where you can 
easily get by with software RAID and use the $300-$400 for more RAM.

Uses for hardware RAID I can think of off the top of my head:

1) Combined CPU/IO loads that exceed the caching ability of your RAM, such as 
databases with a huge working set.  Many people who are in this situation 
have hardware RAID in an external storage device or a SAN anyway, though.

2)  Limited space servers where you only have room for a limited number of 
disks and can't afford the space loss associated with RAID1 or RAID0+1.  You 
can generally only boot from a RAID5 with hardware controllers. (*)

...  uh, that's it.

Brian

(*) Buy a bigger server.