On Wed, 2011-04-06 at 10:51 -0700, Joel Jaeggli wrote: > On 4/6/11 10:38 AM, Jan Ceuleers wrote: > > On 04/04/11 14:33, Francesco Trentini wrote: > >> sorry if this is not the proper channel, but I remember a discussion on > >> Soekris list time ago about the possibility of the inclusion of a simple > >> RAID1 chip on board. > >> > >> Due to the imminent new board 6501, and the presence of two SATA > >> interfaces, this will surely be a very welcomed addition allowing to > >> create a simple mirrored bootable array of two disks. > > > > Francesco, > > > > There is no need for a RAID chip in order to be able to boot from a > > RAID1. I have been doing so in several machines using Linux's md > > capabilities for several years. > > freebsd-geom does the analogous thing, there are a few cases where a > hardware raid controller would do a better job of hiding the failed disk > from the bios, but I have survived primary disk failure including across > reboots and with a newly inserted unformatted drive both in testing and > in the field with both geom and md. a better protection in the case of a > device like the soekris (and where you're trying to protect the contents > of primary storage. would be to put the boot directory/code on a small > flash and raid the primary storage. that's a lot cheaper than even the > cheapest lsi raid-chipset, and probably fits the "good enough" category > pretty well.
There has been discussions about whether hardware or software RAID is the 'best'. In my own systems, I have switched away from hardware RAID as it seemed to be machine specific - i.e., if bad things happen, it is difficult to mount half of a bad RAID1 array on another machine to recover the data. With software RAID, hardware compatibility issues in the case of a crash are not as severe. > > > I am not often able to test whether the machine boots when one of the > > mirror disks has failed (as opposed to just being absent), but on the > > few occasions where this was the case it has indeed worked properly. > > > > Cheers, Jan > > Testing is one of those things that you wished you had done a better job of in the past. Testing RAID arrays can be done by just pulling the data cable to one of the disks - then watch what happens. Then power cycle to see if you have written the MBR to the 'good' disk. Then power down, plug in the data cable, boot up and see if the 'new' disk is rebuilt. Then repeat - pulling the data wire from the other disk. Usually, you discover that the 'good' disk is unbootable because the MBR really was not written to that disk. Or, your bios is fixed to boot off the 'first' hard disk. A simple cable swap will fix that problem. _______________________________________________ Soekris-tech mailing list [email protected] http://lists.soekris.com/mailman/listinfo/soekris-tech
