"Bryan J. Smith" thebs413@earthlink.net wrote:
Hold on a second ... Are you using a SCSI backplane? If so, that's the difference right there! ;-> SCSI backplanes and host adapters work very, very different on transient (or failure for that matter) than _any_ ATA or regular SCSI (without a backplane). They are still formulating similarly for SATA, and there are some SCSI adopted standards for SATA backplanes. But with SAS, much of that is becoming moot. Okay, now things make far more sense. ;->
Okay, let me put this summary out ...
1) Software RAID with SCSI
If you want reliable software RAID for failed drives or hot-swap drives, you want to get a host adapter _and_ a SCSI backplane that work together. The card must then have full SCSI-2 support via their driver for the SCSI subsystem to enable such disconnect and hot-swap features, which is then paired with the backplane hardware.
2) Hardware RAID with ATA
3Ware Escalade, Areca ARC and other ATA RAID controllers use _true_ hardware RAID by the way of ASIC or microcontrollers that _never_ let the OS see the "raw" disc. When the discs are managed into arrays, the on-board intelligence can handle failures and hot-swaps.
If the discs are not managed as arrays, they report the discs as they are to the OS, which means if they fail or are removed, you'll _lose_ the device. Although these card's drivers might load via the SCSI subsystem, they are _not_ SCSI cards, and do _not_ have a full SCSI-2 feature set.
3) Software RAID with ATA, SCSI (non-backplane) or JBOD modes
You're on your own here. If there is not a full SCSI-2 driver for your controller, with associated hardware to handle loss or transient, then you're likely going to get a panic. The "new option" in kernel 2.6 is allegedly hotswap, but I have never configured a storage device for it -- other than USB, FireWire, CompactFlash, etc...
Now does this make more sense? ;->