6. Supported Hardware & Software

1. Q: I have SCSI adapter brand XYZ (with or without several channels), and disk brand(s) PQR and LMN, will these work with md to create a linear/stripped/mirrored personality?

   A: Yes! Software RAID will work with any disk controller (IDE or SCSI) and any disks. The disks do not have to be identical, nor do the controllers. For example, a RAID mirror can be created with one half the mirror being a SCSI disk, and the other an IDE disk. The disks do not even have to be the same size. There are no restrictions on the mixing & matching of disks and controllers.

   This is because Software RAID works with disk partitions, not with the raw disks themselves. The only recommendation is that for RAID levels 1 and 5, the disk partitions that are used as part of the same set be the same size. If the partitions used to make up the RAID 1 or 5 array are not the same size, then the excess space in the larger partitions is wasted (not used).

2. Q: I have a twin channel BT-952, and the box states that it supports hardware RAID 0, 1 and 0+1. I have made a RAID set with two drives, the card apparently recognizes them when it's doing it's BIOS startup routine. I've been reading in the driver source code, but found no reference to the hardware RAID support. Anybody out there working on that?

   A: The Mylex/BusLogic FlashPoint boards with RAIDPlus are actually software RAID, not hardware RAID at all. RAIDPlus is only supported on Windows 95 and Windows NT, not on Netware or any of the Unix platforms. Aside from booting and configuration, the RAID support is actually in the OS drivers.

   While in theory Linux support for RAIDPlus is possible, the implementation of RAID-0/1/4/5 in the Linux kernel is much more flexible and should have superior performance, so there's little reason to support RAIDPlus directly.

3. Q: I want to run RAID with an SMP box. Is RAID SMP-safe?

   A: "I think so" is the best answer available at the time I write this (April 98). A number of users report that they have been using RAID with SMP for nearly a year, without problems. However, as of April 98 (circa kernel 2.1.9x), the following problems have been noted on the mailing list:

   • Adaptec AIC7xxx SCSI drivers are not SMP safe (General note: Adaptec adapters have a long & lengthly history of problems & flakiness in general. Although they seem to be the most easily available, widespread and cheapest SCSI adapters, they should be avoided. After factoring for time lost, frustration, and corrupted data, Adaptec's will prove to be the costliest mistake you'll ever make. That said, if you have SMP problems with 2.1.88, try the patch ftp://ftp.bero-online.ml.org/pub/linux/aic7xxx-5.0.7-linux21.tar.gz I am not sure if this patch has been pulled into later 2.1.x kernels. For further info, take a look at the mail archives for March 98 at http://www.linuxhq.com/lnxlists/linux-raid/lr_9803_01/ As usual, due to the rapidly changing nature of the latest experimental 2.1.x kernels, the problems described in these mailing lists may or may not have been fixed by the time your read this. Caveat Emptor. )
   • IO-APIC with RAID-0 on SMP has been reported to crash in 2.1.90