Linux DPT Hardware RAID HOWTO
  Ram Samudrala (me@ram.org)
  v1.1,  December 15, 1997

  How to set up hardware RAID under Linux.

  1.  Introduction

  This document describes how to set up SCSI hardware RAID, focusing
  mainly on host-based adapters from DPT, though the principles applied
  here are fairly general.

  Use the information below at your own risk.  I disclaim all
  responsibility for anything you may do after reading this HOWTO. The
  latest version of this HOWTO will always be available at
  http://www.ram.org/computing/linux/dpt_raid.html.

  2.  Supported controllers

  Currently the only well-supported host-based hardware RAID controller
  (i.e, a controller for which there exists a driver under Linux) is one
  that is made by DPT <http://www.dpt.com>. However, there exist other
  host-based and scsi-to-scsi controller which may work under Linux.
  These include the ones made by Syred <http://www.syred.com>, ICP-
  Vortex <http://www.icp-vortex.com>, and BusLogic <http://www.bus-
  logic.com>.  In addition, there exist plenty of SCSI-to-SCSI
  controllers. See the RAID solutions for Linux page
  <http://linas.org/linux/raid.html> for more info.

  If, in the future, there is support for other drivers, I will do my
  best to incorporate that information into this HOWTO.

  3.  What hardware should be used?

  Given all these options, if you're looking for a RAID solution, you
  need to think carefully about what you want.  Depending on what you
  want to do, and which RAID level you wish to use, some cards may be
  better than others.  SCSI-to-SCSI adapters may not be as good as host-
  based adapters, for example (see the DPT comparison between host-based
  and SCSI-to-SCSI adapters <http://www.dpt.com/hstvscsi.html> for why
  this is the case).  Michael Neuffer (neuffer@kralle.zdv.uni-mainz.de),
  the author of the EATA-DMA driver, has a nice discussion about this on
  his Linux High Performance SCSI and RAID page <http://www.uni-
  mainz.de/~neuffer/scsi/>.

  For the purposes of this HOWTO, I am assuming you have only a Linux
  system running. Also, note that I've only tried this out with the DPT
  Smartcache VI PM2144UW controller, with the DPT-supplied enclosure
  (SmartRAID tower), and I have no experience with other set ups. So
  things may be different for your setup.

  4.  Installation

  4.1.  Installing and configuring the hardware

  Refer to the instruction manual to install the card and the drives.
  For DPT, since a storage manager for Linux doesn't exist yet, you need
  to create a MS-DOS-formatted disk with the system on it (usually
  created using the command "format \s" at the MS-DOS prompt).  You will
  also be using the DPT storage manager for MS-DOS, which you should
  probably make a copy of for safety.

  Once the hardware is in place, boot using the DOS system disk. Replace
  the DOS disk with the storage manager. And invoke the storage manager
  using the command:

       a:\ dptmgr

  Wait a minute or so, and you'll get a nice menu of options.  Configure
  the set of disks as a hardware RAID (single logical array). Choose
  "other" as the operating system.

  The MS-DOS storage manager is a lot easier to use with a mouse, and so
  you might want to have a mouse driver on the initial system disk you
  create.

  Technically, it should be possible to run the SCO storage manager
  under Linux, but it may be more trouble than its worth.  It's probably
  more easier to run the MS-DOS storage manager under Linux.

  4.2.  Configuring the kernel

  You will need to configure the kernel with SCSI support and the
  appropriate low level driver.  See the Kernel HOWTO
  <http://sunsite.unc.edu/mdw/HOWTO/Kernel-HOWTO.html> for information
  on how to compile the kernel. Once you choose "yes" for SCSI support,
  in the low level drivers section, select the driver of your choice
  (EATA-DMA for most EATA-DMA compliant (DPT) cards, EATA-PIO for the
  very old PM2001 and PM2012A from DPT).  Most drivers, including the
  EATA-DMA driver, should be available in recent kernel versions.

  Once you have the kernel compiled, reboot, and if you've set up
  everything correctly, you should see the driver recognising the RAID
  as a single SCSI disk. If you use RAID-5, you will see the size of
  this disk to be 2/3 of the actual disk space available.  The messages
  you see upon bootup should look something like this:

       EATA (Extended Attachment) driver version: 2.59b
       developed in co-operation with DPT
       (c) 1993-96 Michael Neuffer, mike@i-Connect.Net
       Registered HBAs:
       HBA no. Boardtype    Revis  EATA Bus  BaseIO IRQ DMA Ch ID Pr QS  S/G IS
       scsi0 : PM2144UW     v07L.Y 2.0c PCI  0xef90  11 BMST 1  7  N  64 252 Y
       scsi0 : EATA (Extended Attachment) HBA driver
       scsi : 1 host.
         Vendor: DPT       Model: RAID-5            Rev: 07LY
         Type:   Direct-Access                      ANSI SCSI revision: 02
       Detected scsi disk sda at scsi0, channel 0, id 8, lun 0
       scsi0: queue depth for target 8 on channel 0 set to 64
       scsi : detected 1 SCSI disk total.
       SCSI device sda: hdwr sector= 512 bytes. Sectors= 35591040 [17378 MB] [17.4 GB]

  (The above display is for a setup with a single DPT SCSI controller,
  configured as RAID-5, with three disks of 9 GB each.)

  5.  Usage

  5.1.  fdisk, mke2fs, mount, etc.

  You can now start treating the RAID as a regular disk. The first thing
  you'll need to do is partition the disk (using fdisk).  You'll then
  need to set up an ext2 filesystem.  This can be done by running the
  command:

       % mkfs -t ext2 /dev/sdxN

  where /dev/sdxN is the name of the SCSI partition.  Once you do this,
  you'll be able to mount the partitions and use them as you would any
  other disk (including adding entries in /etc/fstab).

  5.2.  Hotswapping

  We first tried to test hotswapping by removing a drive and putting it
  back in the DPT-supplied enclosure/tower (which you buy for an
  additional cost).  Before we could carry this out to completion, one
  of the disks failed (as I write this, the beeping is driving me
  crazy). Even though one of the disks failed, all the data on the RAID
  drive is accessible.

  Instead of replacing the drive, we just went through the motions and
  put the same drive back in.  The drive rebuilt itself and everything
  seems to be okay.  During the time the disk had filed, and during the
  rebuilding process, all the data was accessible. Though it should be
  noted that if another disk had failed, we'd have been in serious
  trouble.

  5.3.  Performance

  Here's the output of the Bonnie program, on a 2144 UW with 9x3=17 GB
  RAID 5 setup. The RAID is on a dual processor Pentium Pro machine
  running Linux 2.0.32. For comparison, the Bonnie results for the IDE
  drive on that machine are also given.

                  -------Sequential Output-------- ---Sequential Input--  --Random--
                  -Per Char- --Block--- -Rewrite-- -Per Char- --Block---  --Seeks---
               MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU   /sec  %CPU
       RAID   100  9210 96.8  1613  5.9   717  5.8  3797 36.1 90931 96.8 4648.2 159.2
       IDE    100  3277 32.0  6325 23.5  2627 18.3  4818 44.8 59697 88.0  575.9  16.3

  It's clear that the RAID is great for block reads and writes (even
  though write performance is degraded by using RAID-5), but it is not
  very good at sequential re-writes.

  6.  Features in the DPT RAID driver

  This section describes some of the commands available under Linux to
  check on the RAID configuration.  Again, while references to the
  eata_dma driver is made, this can be used to check up on any driver.

  To see the configuration for your driver, type:

       % cat /proc/scsi/eata_dma/N

  where N is the host id for the controller.  You should see something
  like this:

       EATA (Extended Attachment) driver version: 2.59b
       queued commands:         353969
       processed interrupts:    353969

       scsi0 : HBA PM2144UW
       Firmware revision: v07L.Y
       Hardware Configuration:
       IRQ: 11, level triggered
       DMA: BUSMASTER
       CPU: MC68020 20MHz
       Base IO : 0xef90
       Host Bus: PCI
       SCSI Bus: WIDE Speed: 10MB/sec.
       SCSI channel expansion Module: not present
       SmartRAID hardware: present.
           Type: integrated
           Max array groups:              7
           Max drives per RAID 0 array:   7
           Max drives per RAID 3/5 array: 7
       Cache Module: present.

           Type: 0
           Bank0: 16MB without ECC
           Bank1: 0MB without ECC
           Bank2: 0MB without ECC
           Bank3: 0MB without ECC
       Timer Mod.: present
       NVRAM     : present
       SmartROM  : enabled
       Alarm     : on
       Host<->Disk command statistics:
                Reads:      Writes:
           1k:           0            0
           2k:           0            0
           4k:           0            0
           8k:           0            0
          16k:           0            0
          32k:           0            0
          64k:           0            0
         128k:           0            0
         256k:           0            0
         512k:           0            0
        1024k:           0            0
       >1024k:           0            0
       Sum   :           0            0

  To get advanced command statistics, type:

       % echo "eata_dma latency" > /proc/scsi/eata_dma/N

  Then you can do a:

       % cat /proc/scsi/eata_dma/N

  to get more detailed statistics.

  To turn off advanced command statistics, type:

       % echo "eata_dma nolatency" > /proc/scsi/eata_dma/N

  7.  Troubleshooting

  7.1.  Upon bootup, no SCSI hosts are detected

  This could be due to several reasons, but it's probably because the
  appropriate driver is not configured in the kernel. Check and make
  sure the appropriate driver (EATA-DMA for most DPT cards) is
  configured.

  7.2.  RAID configuration shows up as N different disks

  The RAID has not been configured properly.  If you're using a DPT
  storage manager, you need to configure the RAID disks as a single
  logical array.  Michael Neuffer (neuffer@kralle.zdv.uni-mainz.de)
  writes "When you configure the controller with the SM start it with
  the parameter /FW0 and/or select Solaris as OS. This will cause the
  array to be setup to be managed internally by the controller."

  7.3.  If all fails...

  Read the SCSI-HOWTO again.  Check the cabling and the termination.
  Try a different machine if you have access to one.  The most common
  cause of problems with SCSI devices and drivers is because of faulty
  or misconfigured hardware.  Finally, you can post to the various
  newsgroups or e-mail me, and I'll do my best to get back to you.

  8.  References

  The following documents may prove useful to you as you set up RAID:

  �  DPT RAID Primer and other RAID/SCSI-related documents
     <http://www.dpt.com/techno.html>

  �  EATA-DMA homepage <http://www.uni-
     mainz.de/~neuffer/scsi/dpt/index.html>

  �  Linux Disk HOWTO <http://sunsite.unc.edu/mdw/HOWTO/Disk-HOWTO.html>

  �  Linux Kernel HOWTO <http://sunsite.unc.edu/mdw/HOWTO/Kernel-
     HOWTO.html>

  �  Linux SCSI HOWTO <http://sunsite.unc.edu/mdw/HOWTO/SCSI-HOWTO.html>

  �  RAID Solutions for Linux <http://linas.org/linux/raid.html>

  9.  Acknowledgements

  The following people have been helpful in getting this HOWTO done:

  �  Boris Fain (fain@zen.stanford.edu)

  �  Jos Vos (jos@xos.nl)

  �  Michael Neuffer (neuffer@kralle.zdv.uni-mainz.de)

  �  Ralph Wallace (rwallace@rwallace.interaccess.com)

  �  Russell Brown (russell@lutton.lls.com)

  �  Syunsuke Ogata (Syunsuke_Ogata@appear.ne.jp)