PC Hardware in a Nutshell, 3rd Edition [Electronic resources] نسخه متنی

9.3 Installing and Configuring a Tape Drive

External
tape drives are "installed" simply
by connecting them to the parallel, SCSI, USB, or FireWire port, as
appropriate, and connecting power, although you may have to set
jumpers to configure a SCSI drive for the proper SCSI ID and
termination. Internal tape drives are 3.5- or 5.25-inch half-height
devices, and require the same physical installation steps as any
other externally accessible drive. The exact configuration steps
required differ between ATAPI and SCSI interfaces, as described in
the following sections.

Some tape drive manufacturers, including Seagate, recommend installing the backup software before installing the tape drive. But do not run the backup software before the drive is installed and recognized by the computer and operating system, or you may find that you need to reinstall the backup software in order for it to recognize the drive. Microsoft Backup has burned us this way more than once. Conversely, some tape backup softwaretypically that bundled with a tape driverefuses to install unless a tape drive that it supports is already installed. Read the manual for the tape drive and the backup software before you begin the installation.

9.3.1 Installing and Configuring an ATAPI Tape Drive

ATAPI tape drives are physically
installed and configured just like any other ATAPI/IDE device: set
the drive's Master/Slave jumper; secure the drive in
an available drive bay using four screws; connect the data cable,
aligning Pin 1 on the drive connector with the colored stripe on the
cable; and connect the power cable. Note the following issues when
installing an ATAPI tape drive:

Installing a tape drive on the same IDE channel as a hard disk risks
data corruption. If the system has one hard disk, install it as the
Primary Master and the tape drive on the Secondary channel. If the
system has two hard disks, install both on the Primary channel, and
install the tape drive on the Secondary channel. Do not install three
ATA hard disks in a system with an ATAPI tape drive. If the system
has an ATAPI CD-ROM drive, make that drive Secondary Master and the
tape drive Secondary Slave. If the system has no ATAPI CD-ROM drive,
make the tape drive Secondary Master.

Some tape drives have configuration jumpers to enable such things as
hardware compression, read-while-write, DMA/PIO mode, and emulation
mode. If your drive has one or more of these jumpers, set them as
follows:

Hardware compression





Ordinarily, enable this option to allow the drive itself to compress
the data stream before recording it to tape, but note that software
compression is sometimes more efficient than hardware compression. If
you enable hardware compression, disable compression in your backup
utility. Leaving both enabled results in
"churning" that can actually
increase the size of the data being written to tape. Some backup
utilities have a configuration checkbox that allows you to select
hardware compression. We've never been entirely sure
of the purpose of this checkbox because hardware compression is (or
should be) transparent to the backup application, but if your backup
utility has such a checkbox, it's probably a good
idea to mark it if you enable hardware compression on the drive.

Although different drive models from a particular manufacturer may supposedly use compatible hardware compression, any tape made with hardware compression enabled may be unreadable except in the drive that wrote it. There is no guarantee that you will be able to read a hardware-compressed tape made on one drive with any other drive. Something as subtle as a minor difference in firmware revision may prevent reading a compressed tape even in a seemingly identical drive.




Read-while-write





If your drive has a jumper to enable read-while-write, doing so
allows the drive to use its separate read head to read and verify
data immediately after it is written, avoiding the need for a
time-consuming second compare pass. Not all backup software supports
this function. If your backup software does support it, you may need
to enable support for it within the backup program.




DMA/PIO mode





DMA mode increases throughput and reduces CPU utilization, but not
all tape drives can operate in DMA mode. If your drive is
DMA-capable, it may have a jumper to configure the drive for DMA mode
versus PIO mode. In general, if the tape drive is the only device on
the ATA channel, or if the other device on that channel is also
DMA-capable, enable DMA mode for the tape drive and enable DMA
support for that channel in the operating system. If the tape drive
shares the channel with a PIO-only device (e.g., an older CD-ROM
drive), disable DMA mode for the tape drive or (better) replace the
other device with a DMA-capable device.




Emulation mode





Some tape drives can emulate other drives via a jumper setting that
causes the drive to return incorrect identification data to the
operating system. For example, we have an old Tecmar Travan NS20 tape
drive that was jumpered by default to identify itself as a Wangtek
Model 51000. Removing this jumper causes the drive to identify itself
as a Tecmar Travan NS20. Using emulation allows a new drive model to
be used with older software that does not support the new model. Set
this jumper, if present, according to the
manufacturer's instructions.




Recent BIOSes allow setting boot sequence to first attempt booting
from a CD-ROM drive. What this actually tells the system is to boot
from the first ATAPI device. If an ATAPI tape drive is configured as
Master (even on the Secondary channel), a system so configured may
attempt to boot from the tape drive, which causes the system to hang.
You can avoid this problem by setting the CD-ROM drive to Secondary
Master and the tape drive to Secondary Slave. This problem may also
occur if the tape drive is the only device on the Secondary channel,
whether it is configured as Master or Slave. If you cannot correct
the configuration or disable CD-ROM boot in BIOS, boot the system
with no tape in the drive.

9.3.2 Installing and Configuring a SCSI Tape Drive

Installing and configuring a SCSI
tape drive is a bit more complicated than installing an ATAPI model.
Rather than attempting to provide step-by-step instructions, which
vary according to the specific drive and adapter,
we've chosen to illustrate a typical installation
using a Seagate Hornet NS20 drive and an Adaptec 2930 SCSI host
adapter, both representative selections.

If you have not already done so, install the SCSI host adapter. To do
so, power down the system, remove the cover, and locate an available
bus-mastering PCI slot. (Some older systems don't
support bus mastering on all slots. Bus-mastering slots are usually
white or ivory; non-bus-mastering slots are brown or black.) Remove
the slot cover for the selected slot, align the bus connector with
the slot, and press down firmly to seat the adapter. Use the screw
that secured the slot cover to secure the adapter. If you have a
spare drive activity indicator LED, connect it to J2 on the host
adapter to indicate SCSI bus activity.

The Adaptec host adapter supports SCAM
(SCSI Configured Auto-Magically)a kind of
Plug and Play for SCSI that automatically configures SCSI ID and
termination. (SCAM is described in Section 10.4).
Like most tape drives, the Seagate Travan NS20 does not support SCAM,
so we'll have to set jumpers manually to assign SCSI
ID and set termination.

Like most manually configured SCSI devices, the Seagate Travan NS20
drive has three jumpersID0 (SCSI ID 1), ID1 (SCSI ID 2), and
ID2 (SCSI ID 4). Installing jumper blocks on zero or more of these
jumpers allows you to set SCSI IDs 0 through 7. Connecting no jumpers
assigns SCSI ID 0. Connecting one jumper assigns the SCSI ID
associated with that jumper (e.g., ID1 assigns SCSI ID 2). Connecting
two jumpers assigns the SCSI ID that is the sum of the two jumpers
(e.g., ID0 and ID2 sums the SCSI IDs 1 and 4 to assign the SCSI ID
5). Connecting all three jumpers assigns SCSI ID 7. Like most SCSI
tape drives that require the SCSI ID to be assigned manually, the
Seagate Travan NS20 drive by default is jumpered to SCSI ID 4, which
is usually not in use by other devices.

Avoid setting a tape drive to SCSI ID 0, 1, or 7. ID 0 is reserved by convention for a bootable hard drive, ID 1 for a second hard drive, and ID 7 for the host adapter.

The
Seagate Travan NS20 drive also requires setting termination manually.
Exactly two devices must be terminated on each SCSI bus, and these
devices must be those at each end of the bus, as follows:

If the SCSI adapter has only internal
devices attached to it, the adapter itself and the final device on
the internal SCSI chain must be terminated.

If the SCSI adapter has only external
devices attached to it, the adapter itself and the final device on
the external SCSI chain must be terminated.

If the SCSI adapter has both internal and
external devices attached to it, the adapter must not be terminated.
Instead, terminate the final internal device and the final external
device attached to the SCSI chain.

In this case, the Seagate tape drive is the final device on the
internal SCSI chain, which has no external devices, so the drive and
the host adapter must both be terminated. By default, Pins 3 and 4 on
the drive are jumpered, which terminates it. That's
the correct setting, so we leave it as is. If we were installing the
Seagate Travan NS20 between two existing SCSI devices,
we'd remove the jumper from Pins 3 and 4 to disable
termination.

Pins 1 and 2 are also jumpered by default,
which enables Termination Power. Again, that's the
correct setting, so we leave it at default. Pins 5/6 and 7/8 are
reserved on this drive, so we leave them unjumpered, which is the
default. Pins 9/10 are jumpered, which enables Parity Checking.
Again, that's the correct setting, so we leave it at
default.

Most drives ship with Termination Power and Parity Checking enabled, which is usually correct. If you have trouble accessing a tape drive, check the host adapter manual to determine if Termination Power and/or Parity Checking should be disabled.

Adaptec host
adapters, which we use and recommend exclusively, by default
automatically detect terminated SCSI devices on the bus and set their
own termination status accordingly, so no further action is required
to configure the drive properly. Note that a few internal SCSI cables
have a built-in terminator at the end of the cable. If you use such a
cable, make sure that termination is disabled on all drives connected
to that cable.

Once you have
resolved SCSI ID and termination issues and have the drive physically
installed, the next step is to connect the cables. Most adapters are
supplied with a standard two-device cable. If you need to connect
more than two drives, replace the cable before proceeding. Otherwise,
connect the cable to each drive, making sure to align Pin 1 on the
cable (indicated by a red stripe) with Pin 1 on each device
(indicated by a small number, triangle, or dot on the connector). For
SCSI IDs, it doesn't matter which drive connects to
which cable position, so mix and match drives and cable positions in
whatever way makes it easiest to route the cable. Just make sure that
the physical last drive on the cable is the one
that's terminated. Connect the power cable.

After verifying all settings and
connections, turn on any external SCSI device(s) first, and then turn
on the PC. Ordinarily, the system should boot normally, but the SCSI
tape drive may or may not be recognized, depending on the drive
itself, your operating system, and other factors. Before you
configure the operating system to use the drive, some systems may
require one or both of the following steps:

CMOS Setup





On most systems, the PCI bus assigns IRQs and port addresses
automatically. If your system requires setting PCI bus parameters
manually, do so during the first restart, using the system or
motherboard documentation for guidance. (If your system BIOS is
capable of assigning IRQs automatically, there will usually be a CMOS
Setup option worded something like "Plug and Play
OS?" If that option is set to No, the PC BIOS
assigns IRQs. If it is set to Yes, the BIOS allows the Plug and Play
capable OS [Windows 9X/2000/XP/Linux] to assign IRQs).




SCSI Setup





At boot time, the SCSI BIOS displays adapter and BIOS information and
a list of installed SCSI devices. Ordinarily, the default settings
are fine, but in some cases you may need to change settings to get
the drive to work at all or to optimize its performance. If this is
the case for your system, press whatever key sequence is needed to
invoke the SCSI Setup routine and make the necessary changes, as
recommended by the documentation for the host adapter and/or drive.




If either or both of these steps are needed, restart the system after
completing each. After you complete these steps, the system should
boot normally and physically recognize the tape drive.

9.3.3 Configuring Windows 9X/2000/XP to Support a Tape Drive

Windows 9X/2000/XP does not support

any tape drives in the usual sense, although it
may or may not recognize and display the name of an installed tape
drive, depending on the drive and the version of Windows. Unlike most
other devices, for which drivers are readily available and can be
installed using the Add New Hardware Wizard, tape drives running
under Windows depend on device support built into the backup
application itself. This is why, for example, the Windows 98
Microsoft Backup appletan OEM version of Veritas Backup
Execcan use some tape drives and not others: the program
itself contains drivers for the supported tape drives. All this
really means is that you can't use unsupported
drives with the built-in backup applet. That's not
usually a problem because most tape drives are bundled with backup
software considerably superior to the Windows Backup applet.

Windows support for tape drives is analogous to Windows support for CD writers and DVD writers. Windows recognizes that the drive is present, but has no idea how to exploit its capabilities. Just as with CD/DVD writers, that functionality must be built into application software designed to support the drive, whether that application is supplied by a third party or comes as a Windows applet (as does the Windows Backup application or the limited CD burning application bundled with Windows XP). The backup software bundled with your tape drive will support it. If you buy a bare drive, you'll need to purchase backup software separately, unless the Windows Backup applet supports your drive and is sufficient for your needs.

Recent versions of third-party
Windows backup applications include drivers for many recent-model
tape drives. Most tape drives bundle a competent backup
utilityoften a special version of Backup Exec or
ARCservethat contains the necessary drivers to support that
drive under the operating systems intended to run them. You may,
however, need to download drivers for a new tape drive either from
the tape drive manufacturer (most of which do not supply drivers) or
from the backup software company, if one of the following is true:

You have a previously
purchased backup utility that does not contain drivers for the new
drive.

You have a backup utility
you want to continue to use that was originally bundled with a drive
you are replacing, and that backup utility has no support for the new
drive.

The backup application
supplied with the new drive does not support the operating system you
are using.

Before you
purchase a tape drive for use with Windows, verify that the backup
application you intend to use has drivers for that tape drive.

9.3.4 Configuring Linux to Support a Tape Drive

The ease of configuring
Linux to support a tape drive depends on the Linux distribution and
version, the type of drive, the interface it uses, and whether the
drive is present when Linux is installed or is added later. If you
use a modern, mainstream ATAPI or SCSI drive with a recent Linux
distribution, installation will likely be straightforward. If you use
an older distribution, an obsolescent or proprietary drive, or a
drive that uses an interface other than ATAPI or SCSI, you may
encounter significant problems getting the drive to work, if indeed
you can get it working at all. You can use the following tape drives
with Linux:

Recent Linux releases natively support a wide variety of Travan, DDS,
and AIT tape drives with ATAPI or SCSI interfaces. If you install and
configure the drive and interface properly before you install Linux,
the Linux installer will likely recognize the drive and automatically
configure Linux to use it. In fact, Linux often does a better job
than Windows 2000/XP of recognizing and configuring Travan, DDS, and
AIT tape drives.

If you install a tape drive in a system with Linux already installed,
log in as root and run the hardware detection utility (e.g., Kudzu in
Redhat or Mandrake and Discover in Debian). If the drive is
supported, the utility detects the drive, installs drivers, and
automatically configures Linux to use the drive. If the drive is not
recognized, check the web sites for the drive and your Linux distro
to determine how to configure the drive manually.

USB and FireWire (IEEE-1394) drives require a 2.4 or higher Linux kernel.

Linux support for OnStream tape drives differs according to the
command set used by the drive. All second-generation
(ADR²) drives and first-generation (ADR)
ADR30, ADR50, and ADR50e SCSI drives use the standard SCSI command
set, so the standard st (SCSI tape) driver
suffices to interface the drive to the backup application (the ATAPI
ADR2.60IDE drive requires both the ide-scsi and
st drivers).

Most first-generation OnStream ADR drivesthe DI30, DI30 FAST,
DP30, USB30, SC30, SC30e, SC50, SC50e, and FW30use a
proprietary command set that optimizes those drives for storing
streaming video. That command set differs significantly from the
standard ATAPI and SCSI command sets, which means the standard
st driver does not support these drives. Full (or
even partial) Linux support requires a kernel rebuild or various
workarounds. Fortunately, a modified version of the
st driver, called the osst
driver, is available. The osst driver interfaces
standard backup applications to the proprietary command set of older
ADR drives.

Although the ide-tape driver supports the OnStream DI30 drive, we strongly recommend using the ide-scsi and osst drivers instead. The ide-tape driver writes tapes in LIN3 logical format, whereas osst writes tapes in LIN4 logical format. That means the osst driver reads tapes written with ide-tape, but the ide-tape driver cannot read tapes written with osst. Also, various problems have been reported using ide-tape with DI30 drives, ranging from inability to restore files to complete failure to recognize the drive.

Travan TR-3 and earlier QIC drives use the floppy drive controller
(FDC) interface, either directly or in some cases via a parallel port
connection. These drives are now so old that most have been retired,
but if for some reason you must use an FDC-based tape drive on a
Linux system, you may be able to get it running using
ftape. The ftape driver
supports QIC-40, QIC-80, QIC-3010 (TR-2), QIC-3020 (TR-3), Iomega
Ditto 2GB, and Ditto Max drives. For more information about
ftape, see http://www.ibiblio.org/pub/Linux/docs/HOWTO/other-formats/html_single/Ftape-HOWTOl.

We do not recommend using ftape in PCI-based systems, which is to say in any modern system at all. The ftape driver has known incompatibilities with some PCI motherboards. For details, view README.PCI in the ftape distribution.

Once Linux recognizes a tape drive, you can use
bundled Linux applications such as tar,
mt, mtx,
dump, restore, and
cpio to write and read tapes in the drive. You can
also use full-featured backup applications such as BRU (http://www.tolisgroup.com/), Amanda
(http://www.amanda.org/), and
Arkeia (http://www.arkeia.com/)
to implement a formal backup program.

Here are some
useful sites that cover various aspects of using tape drives with
Linux:

http://www.linuxtapecert.org

http://www.tldp.org/LDP/sag/indexl