USB, SCSI, PATA, SATA or whatever, this are buses, and only one device keeps a line down or high from this bus, every device can´t work correct any more. So to be fault resistence, you need two controllers with only one device connected to it, or two controllers connected to every one device (dual channel). So if one controller fails, the device can talk over the other one. And if the device fails, you can HOPE that it won´t keep the two (SCSI) interfaces in a invalid state. On the other hand with two controllers, you have only one systemboard or cpu which can fail too. With raid you can catch device errors like, bad-blocks, disk error, but not that the device/ disk keeps the bus.. (HW Error in the interface circuit).
Tom
Hermann Himmelbauer wrote:
Anyway - what exactly happens when a PATA harddisk dies? Will this only lead to logentries in the syslog, or will this crash the machine due to hardware reasons? Probably there would also be a difference if you would do RAID on the same channel (e.g. hda, hdb) as a mulfunction of one device could jam the whole IDE channel.
The same thing can apply to SCSI, too - I once experienced this myself when a fautly SCSI-CDROM jammed the whole SCSI-bus and crashed my machine.
I hope that SATA will be a lot less critical, it should support hotplugging (at least with SATA 1.1, it's a pity that it's not supported with 1.0 right away) and there is only one device per channel.
- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
