[Nottingham] Big biiig problem regarding IDE-RAID

Graeme Fowler nottingham at mailman.lug.org.uk
Tue Jul 15 15:57:06 2003

On Tue, 15 Jul 2003, Robert Davies wrote:
> There's some nice-ish IDE RAID enclosures with SCSI interfaces, with serial 
> ATA coming hot swap IDE is going to be made simpler, so costs should fall yet 
> more.

Indeed they will, and I look forward to that day with glee :)

> What you're thinking of is very very doable with software RAID.

Almost certainly. However, one very major difference between straight 
kernel-side software RAID and this specific chipset/driver combo seems to be 
that there is much more of the control being done on the chipset, and the 
driver is simply reading results from and sending instructions to it.

It's currently running a rebuild after we forcibly removed a drive during 
runtime (risky yes, but for evaluation purposes extremely useful). The driver 
immediately reported the loss of the disk and degradation of the array. When 
we plugged the drive back in, the driver (and system) "hung up" for about ten 
seconds - because IDE isn't really ready for hot-swap :D - and then came back 
to life, immediately starting a rebuild.

Further tests with further cable disconnections resulted in a system hang!

Upon rebooting, the BIOS gave us the option to either rebuild from within the 
BIOS or to continue booting. Continuation resulted in the system rebuilding 
"backgrounded", with progress reported in /proc/scsi/FastTrack/0

Notably, it's not reporting scads of activity through vmstat or top, so it
appears that the driver is simply saying "invoke rebuild from drive 0 to drive
1" to the chipset, and not troubling itself with the data. Which is handy 
indeed for those who not only need large amounts of resilient space, but also 
need all the grunt to be available all the time. Looks like it'll be approx 60 
minutes for a 120GB mirrored pair.

Rebuild completed at 34MB/s (megabytes, not bits). Which is failry respectable 
for IDE.

> Not bad for 160 GB capacity RAID-10 storage and 5 ethernet ports  :)

Not bad indeed. I can't talk about prices though, sadly.

The system itself, for those who are interested, is an Intel S845WD1-E mobo
with 512MB ECC DDR RAM (expandable to 2GB if you can afford 2*1GB DDR DIMMs)
with 2.4GHz P4, dual onboard EtherExpress Pro 100+ NICs, onboard 64MB Rage 
graphics and onboard Promise IDE RAID.

All in all, it's a very attractive proposition. For a specific job :)