Timothy
Parker Consulting Incorporated
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Tapedrives and Linux The age-old problem of backing up data
onto removable, storable media has been around since the first days of Linux.
Early kernels managed to include drives for basic SCSI tape drives, and
other devices were quickly added to meet the needs of users.
The UNIX field has seen lots of tape drives come and go, with
ever-expanding capacities and speed of backup, while the cost of high-capacity
drives has dropped (although media prices seem still high).
For many of us, backing up many gigabytes of data every night is a
routine we follow, and finding the right backup device is a sometimes-awkward
and difficult process. Solutions
that work well for Windows NT, UNIX, or other operating systems may not work
quite as well for Linux. In this article, we look at the different technologies
available for backup drives, as well as the software that controls your backups. Backup hardware The most traditional tape backup system
is QIC (Quarter Inch Cartridge) but is seldom seen today.
QIC fell out of favor several years ago because of its limited capacity,
large media size, and slowness. Most
QIC tape drives couldn’t pack more than 1GB of data on a cartridge, even with
data compression active, and backups could take many hours.
Although QIC has pushed the length of tapes and hence capacity up above
1GB, QIC is used primarily only in legacy systems that had QIC drives available
from other UNIX systems. The DAT (Digital Audio Tape) backup
system became popular just as QIC was waning.
DAT provided 2GB compressed data storage, which was quickly followed by
4GB on a small cartridge. (All
compressed data figures quoted in this article are assuming an average of 2:1
compression; native capacity is half the compressed value.) Current DAT storage
systems can hold up to 40GB compressed data, although the media costs for the
higher-capacity DAT systems tend to be high.
Lower-capacity DAT tape systems have the advantage of being inexpensive
to buy and a low per-tape media cost. The
speed is not exceptional, but for smaller workstation systems, SCSI-based DAT is
an inexpensive and acceptable solution. Higher-capacity
tape drives, such as Hewlett-Packard’s DAT24e and DAT 40e (24GB and 40GB
compressed storage respectively) are more expensive, and media costs are higher. DAT had an upper capacity limit several
years ago, leading to several other tape drive solutions. Sony’s AIT (Advanced
Intelligent Tape) system was one approach that has been adopted by other
vendors, and continues to be popular today.
AIT uses tapes about the size of a cassette, and stores 50GB compressed
data in a small size. AIT allows
for a feature called MIC (Memory In Cartridge) which uses an embedded memory
chip in the tape cartridge itself to hold the tape’s table of contents.
This allows for faster positioning of the tape for restoration purposes,
but does add to the cost of the media. AIT
systems are small in physical size, but all models available are SCSI-based.
(See sidebar “Sony AIT”) DLT (Digital Linear Tape) is another
alternative, providing 35GB compressed data (recently expanded to 70GB) on a
cartridge reminiscent of 8-track tapes. DLT is an expensive drive system to
purchase and media is expensive, too. Having
said that, DLT is quite fast in both backup and restore capabilities. (See
sidebar “Quantum DLT 8000”) Travan tapes drives have become popular
of late, primarily because of the inexpensive tape drives and reduced media
cost. Travan can be used with SCSI
and IDE interfaces, making it attractive for some workstation users who retain
ATA or IDE hard drives. Travan
cartridges are usually limited in capacity to 20GB compressed data, and are not
very fast, but the Travan system is economical and ideal for workstation users.
(See the sidebar “Travan tape drives”). Two new technologies have emerged in the
last couple of years. Ecrix VXA is
a proprietary system that provides 66GB compressed data. Ecrix’ claim to fame
is the speed and cost comparison of the XVA to other tape systems on the market.
(See sidebar “Ecrix VXA”) The other new technology is the OnStream system
which can hold 50GB of compressed data on a streaming tape cartridge.
Support for OnStream drives, which are available in IDE/ATA and SCSI
versions, is very good under Linux. We couldn’t obtain a review unit of the
latest version of OnStream drives for this article, but the older 35GB drive was
tested and performed slower than the Travan tape drives. Which is the best hardware solution for
you? It depends, as always, on the
budget, your requirements, and the amount of material you back up. The Travan
systems are inexpensive to buy, media is inexpensive, and for smaller
workstations or home units, the speed will not be an issue.
For larger capacity tape drives, the AIT and DLT systems are attractive,
although the latter’s high cost will be prohibitive for all but network
installations. A good compromise is
the Ecrix VXA, although it is proprietary (and you’re at the mercy of one
company for support and supplies) or DAT (long known for its reliability).
Balance the cost of the drive and the cost of each GB backed up against
the data size you need to back up, add a fudge factor if speed is important, and
you’ll find the best backup tape drive for your system. Backup Software Do you need a special backup software
package? If you are backing up only
a few files, tar and cpio will do the trick (if you can master the syntax).
For larger backups, it’s worth the investment to buy a backup software
package. There are many on the
market for Linux, and they differ in features and abilities.
To test backup software, we installed three Linux servers (RedHat 6.2,
Caldera 2.4, and Corel 2.0) with SCSI hard drives, Travan, DLT, and Ecrix tape
backup hardware, and performed several backup and restore cycles.
We wanted to see how easy each of the backup packages was to use, how
efficiently it backed up and restored, and how good it was at reporting status
of backups. Cactus International and Lone Star
Software’s Lone-Tar and Air-Bag products have been used on SCO systems for
over a decade, and now they are available for Linux. Lone-Tar is a command line
and menu-driven front end backup and restore utility while Air-Bag is a bootable
diskette recovery utility. The
software won’t run on all versions of Linux, so check for compatibility with
the vendor before you buy or download. The
software does not feature automatic detection of hardware, so all backup devices
have to be configured manually. Lone-Tar
was not the flashiest product in our tests but the simple interface does perform
backup and restore processes with a minimum of fuss and prompting.
At $69, Lone-Tar for Linux is an attractive option. Enhanced Software Technologies’ BRU
(Backup and Restore Utility) has been around the UNIX world for many years.
The Personal Edition of BRU is intended for non-commercial, non-networked
installations, while the full BRU package is designed for network use. The
differences between BRU-PE and the full version are support for networked
devices, NFS mount support, the ability to backup raw partitions, file rename
during restoration, and double-buffered I/O (which increases speed in the full
version). BRU has a command line
and an X interface but they have to be installed as different products.
Backup devices must be configured manually. The
EST Web site has a page of sample configurations and drivers. BRU includes a
utility called CRU (Crash Recovery Utility) that provides a boot-from-diskette
full system recovery capability. Knox Software’s Arkeia is a package
that stands out immediately because of the attractive (but busy) user interface.
Arkeia supports RedHat, Mandrake and SuSe Linux, as well as generic Linux
and some UNIX platforms. The three software components in the Arkeia package
must be installed in the correct order, one after another.
The configuration process was the most annoying of all the backup
packages tested here. The X interface provided with Arkeia is overwhelming
compared to every other interface we tested.
VU-like meters showing backup speed and disk and tape conditions dominate
the screen. The bottom of the
screen shows updated information about the files being backed up or restored.
You interact with Arkeia through a dialog that lets you click-and-choose
files, directories, or entire disks to back up or restore.
There is a command line interface that is a little faster, but much less
interesting to watch. After working with the Arkeia GUI for a while, you will
realize it’s a waste of time to watch the meters show backup rates but the
interface is fun to watch the first few times. Arkeia uses generic SCSI drivers for
tape control. Under the front end the Arkeia backup system is quite powerful.
Network-wide backups can be performed from different platforms. You can
even place multiple backups from different systems on the same tape. Arkeia
seems ideal for larger systems with network storage devices but may be overkill
for small systems, although at $199 it is not overpriced.
. Microlite BackupEDGE is a well-known
UNIX backup and restore utility that has been ported to Linux.
The BackupEDGE package includes two components, BackupEDGE for backups
and RecoverEDGE for emergency crash recovery. The CD-ROM that accompanies
BackupEDGE includes binaries Linux 2.x versions as well as some other UNIX and
Windows platforms. A wizard
successfully detected all our SCSI devices and this approach will be excellent
for those not comfortable configuring devices on their own.
BackupEDGE uses a character-based interface for all tasks. The menu is
quickly learned and fast to use. A
command line interface for scripting is available, but keeping track of options
and arguments can be difficult. BackupEDGE handles raw partitions, including
those on operating systems that are not natively recognized by the operating
system performing the backup. This
allows complete partition image backups and restores for entire disks that may
contain multiple operating systems, an ideal solution for multiboot Linux
systems. Merlin Software Technologies Perfect
Backup+ is designed for Linux and it takes advantage of the operating system’s
features. The installation and
configuration process take only a few minutes using a package manager.
Especially useful is a detection wizard that detects backup devices and
configures them for you. You can
manually configure devices, too, which will be necessary for network tape
drives. The interface is through X,
although there is a simple command line mode available as well. One-click
buttons let you initiate backup and restore cycles quickly.
A set of “predefined backup packages” target specific applications
and their file storage locations and makes backing up these applications a snap
although the set is limited to common application suites like WordPefect for
Linux and Applix. It’s easy to
see why Perfect Backup+ is becoming the backup utility of choice for Linux
because it seems to cover all the bases at only $69.
The price is fair especially considering the network-capable tool you are
buying. The most expensive package in the backup
and restore tests, Microlite’s BackupEDGE, won all our speed tests, and with
Perfect Backup+ had the best configuration wizards. They both detected our tape drives without problem, and
configuring a network-based backup device was also easy. The most visually
interesting interface belongs to Arkeia, while Merlin’s Perfect Backup+ is
notable for its Linux-centric approach. Of the tools we tested, Microlite’s
BackupEDGE is preferable for its speed and flexibility, but either Arkeia or
Perfect Backup+ will for those looking to spend less and sacrifice a little
speed. (See tape backup vendor sidebar). Wrap up With all these hardware and software
choices, there’s no reason for you not to find a combination of tape backup
drive and controlling software that suits your system requirements and budget.
The easiest way to choose backup hardware is to base the requirements on
amount of data to be backed up regularly. Then,
choose based on speed and price. For
backup software, the most expensive packages we tested were still reasonably
priced, especially considering their capabilities.
While a good backup tape drive and controlling software package are going
to cost you a few dollars, they are cheap compared to the hassle of losing all
your data. Remember the three rules
of system administration: backup, backup and backup! TRAVAN Tape Drives Travan tape backup systems have become
more readily available with 20GB compressed storage,replacing the original 4 or
8GB devices, on reasonably priced cartridges.
Travan units are almost always SCSI-based, although a few are now
sporting ATA interfaces. There are several Travan tape systems on the market,
but a few are notable for their market presence and vendor profiles.
We tested Seagate’s TapeStor 20 (an internal unit) and two external
units (Hewlett-Packard’s SureStore T20e and Tecmar’s Travan NS20) to see if
there is any difference in drives. All three drives were configured on a RedHat
6.2 Linux system using SCSI interfaces. The HP SureStore T20e is the smaller of
the two external units. A CD-ROM
accompanying the drive includes backup software for Windows and Windows NT but
no drivers or support software for Linux (although some is now available from
the HP Web site). The Tecmar
external NS20 had a pair of SCSI-1 connectors on the back of the drive, not the
SCSI-2 of the HP SureStore T20e. One
of the first features you notice with the Tecmar drive is a feature called
iNSync, a motorized loading and ejection mechanism.
The other Travan drives we tested require you to push the cartridge in
all the way, and give it a good tug to remove the cartridge from the drive.
With the Tecmar the tape cartridge is slowly loaded automatically into
the drive unit when the drive senses a cartridge at the slot, and slowly ejects
it after pushing the eject button or a software eject is issued.
It’s a neat feature, but doesn’t affect performance at all. The Seagate TapeStor NS20 internal unit
is smaller than the externals (lacking the bulky case and power transformers)
and can sit in a 3.5inch slot in many cases.
The package we tested came with Seagate’s Backup Exec software (now
sold under the name Veritas Backup Exec) and was designed for Windows.
No dedicated Linux software was included with the Seagate. All three drives performed backup and
restore operations within a few percentage points of each other.
A 20GB backup took 130 minutes plus or minus five minutes. In
uncompressed mode, backups were slower still. Since the limiting factor in
backup time is the speed at which data is written on the tape media, not the
speed at which it can be sent to the Travan unit, this is what you would expect.
Compression is performed in the tape drive itself, not in the backup software,
so there’s no problem using compressed tapes and moving them to another
system. Restored
times of files from both the beginning and end of the tape were within a
few seconds of each other again showing no real performance differences. How does Travan compare to AIT, DLT
and DAT backups? We timed similar backups from the Seagate Travan tape drive,
a Sony SXC-300 AIT, a Quantum DLT 8000, and a Hewlett-Packard SureStore 24 DAT
drive. The AIT drive was the
fastest of the three, followed by the DLT and DAT drives close together, then
the Travan drive quite a bit slower. For
a 20GB backup the AIT (50GB capacity) took just under one hour, the DLT (70GB
capacity) took eighty-five minutes, the DAT drive (24GB capacity) ninety
minutes, and the Travan (20GB capacity) just over two hours.
The Ecrix VXA was tested later, and proved faster than even the AIT
drive. Keeping in mind that the AIT drive is four times as expensive as the
Travan, the DLT is four times as much, and the DAT is twice as much you quickly
can balance the cost against performance for each of these units.
Most Travan external units are now hovering around $350 to $450 in price. SureStore T20e TapeStor 20 Tecmar Travan NS20 Ecrix VXA Tape Drive The Ecrix VXA tape unit offers 66GB of
storage backed up at an average of 6MBbps. With the tape drive listing at $899
($1049 external), the Ecrix VXA offers a better price-per-gigabyte than most
other tape formats available. The
Ecrix VXA external drive is two inches high, six inches wide, and 8 inches deep,
larger than a Travan or DAT drive, smaller than a DLT drive.
The back panel’s dual SCSI-2 connectors can run in single-ended, fast
and narrow, or Ultra LVD formats of SCSI-2. The Ecrix VXA tapes are similar to DAT
cartridges in size. Ecrix touts their tape technology as being radical, and is
divided into three area: Discrete Packet Format (DPF) controls the way data is
written in packets to the tape; Variable Speed Operation (VSO) adjusts tape
speed to match data write or read requirements; and OverScan Operation (OSO)
allows data to be read without regard to track geometry or layout and allows
overscanning of damaged tape areas. The Ecrix VXA works under several
operating systems including Linux (such as SCO OpenServer, SCO UnixWare, and
Windows NT). No special drivers are needed as the drive can be configured as a
standard SCSI tape device, although a CD-ROM supplied with the VXA does include
drivers. The cost of tape media is
lower than other tape drives mentioned in this article, although they are
available only from very limited sources (with the primary source being Ecrix
where media can be ordered through a Web site).
The tape drive itself is cheaper than competing high-capacity drives such
as DLT and AIT drive. The speed of the Ecrix VXA is notable in
comparison with other tape formats. We consistently managed to back up between
60 and 66GB of data to an Ecrix tape, regardless of the type of data.
We backed up 60GB of data in three hours, about the same amount of time
it took a Sony AIT drive to back up 25GB! Recovery
of files was fast, too, averaging less than a minute for a file at the beginning
of the backup and five minutes for a file at the end of the tape.
One of the strengths of the Ecrix VXA is handling damaged tape. Those
readers who have worked on UNIX and Linux systems for years know the dreaded
“media error” that renders a tape backup useless beyond the media flaw. The
Ecrix VXA keeps on reading media after any bad blocks. The Ecrix VXA tape drive is considerably
less expensive than competing DLT and AIT drives. The media cost-per-gigabyte of
storage is a third that of DAT, and a quarter that of AIT and DLT.
With support for Linux, this is an attractive, if proprietary, approach
to high-capacity tape backups. The Ecrix VXA is selling for around $989 from the
company Web site. Ecrix VXA HP SureStore DAT24e and DAT 40e DAT has been available for many years,
and Hewlett-Packard keeps pushing the capacity limits of DAT higher and higher.
A couple of years ago, HP introduced the SureStore DAT24 drive that
allows 24GB (compressed) on a single DDS-3 tape and now offers the DAT40e with
40GB (compressed) on a DDS-4 tape. DDS-3 and DDS-4 DAT tapes are designed for
those specific capacities although there is the ability to use any tape in
either drive, but not with the full capacity available. Older DAT drives
including previous HP SureStore DAT units use DDS-2 tapes, which has an upper
limit of 8GB compressed capacity. Out of the box, the DAT24 and DAT 40
external drives look like all the other SureStore DAT drives.
The rear of the external drives uses SCSI-2.
The software packaged with the DAT24 and DAT 40 is Windows-specific, but
as with all SCSI tape devices it works with Linux as a generic tape device. Some
Linux-specific drivers are available from support sites.
The head cleaner for the DAT24 and DAT 40 is built into the unit,
eliminating the cleaning ritual.
With list prices around $1,400, the SureStore DAT drives are not
inexpensive, but also not in the same price category as DLT. The media costs
tend to be notably lower than other tape backups, and DAT is widely used. DAT
also has a long and notable history of providing solid, reliable backups for
UNIX and Linux systems. DAT24e and DAT 40e Quantum DLT 8000 Like all DLT units, the Quantum DLT 8000
is a big, clunky piece of equipment. It’s also one of the most expensive tape
backup units on the market. (Some
vendors, notably Transitional Technology Inc. have tried to offer much more
reasonably priced DLT subsystems, but few have managed to stay in business long
enough to compete with Quantum, HP and other DLT mainstream vendors.) The DLT
8000 provides for 80GB compressed data storage, and uses the SCSI interface. No
IDE/ATA interface seems to be available for DLT drives. The DLT 8000 is a well-built unit, and
will probably outlast any system it is attached to.
The DLT tapes themselves used half-inch tape inside their squarish
containers. DLT treats tape
different than other formats mentioned in this article in that with DLT the tape
is extracted from the cartridge and wound around transport and head mechanisms
(much like a VHS tape unit). AIT,
DAT and Travan all place heads and transport rollers in contact with the
cartridge, leaving the tape inside the cartridge at all times. While the DLT approach may seem more prone to failure and
problems, DLT has proven to be reliable and robust. The only real problems with
this approach to tape handling is when the cartridge is hauled out of the tape
drive without rewinding (ruined tape is the result) or a power failure screws up
the mechanism and tape gets wound around internal components or gets stuck
(again, a ruined tape). A UPS is
mandatory to prevent this type of problem. For the high cost of the unit, DLT
doesn’t really surpass any other media in speed.
The backup and restore times of the Quantum DLT 8000 are about the same
as those for AIT drives, and slower than those for Ecrix VXA backups. The main
attraction of the Quantum DLT 8000 is its high capacity (the highest of current
backup systems) and the ability to use autoloaders to automate many backup
functions. At $4,700 for the DLT
8000, this is not a trivial purchase, and will probably be overkill for all but
the most complex Linux installation. Quantum Corporation Sony AIT Tape Drive The AIT (Advanced Intelligent
Tape) drives from Sony have evolved the last few years from earlier units to
more sophisticated drives with higher capacities. Sony got 50GB compressed data
on a cartridge with the first generation of units, and now offers 70GB
compressed data on the later models. One key to AIT’s performance and speed is
a memory chip embedded in the cartridge which holds 16kb of data and contains
the cartridge’s log. The tape in
the cartridges is 8mm wide and uses a metal evaporation manufacturing process
for high particle density. Of the tape drives tested in this
review, the AIT was the second fastest, falling behind the Ecrix VXA for
backups, but rivalling the Ecrix for restore operations. The SCSI interface
provides relatively fast throughout, but the drive really needs good backup
software to control it and take advantage of its features.
Although Sony has drivers for several operating systems available on
their company Web site, support for Linux is still a little spotty.
Indeed, support for the AIT is loose, as it doesn’t seem to be making
quite the hit Sony hoped for several years ago. AIT drives are not cheap,
costing several thousand dollars each (even when OEMed to other vendors). Sony Corporation of America Sidebar: Tape Backup software vendors Lone-Tar EST BRU BackupEDGE Arkeia Perfect Backup+ |
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