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Mass Storage: Network Storage
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Future Horizons
Two of the hot new network storage management
buzzwords are Network Attached Storage (NAS)
and Storage Area Network (SAN). An NAS device is
designed to connect anywhere on the network, and
it doesn't rely on a server to provide access to the
data. In the most basic sense, an NAS "network
appliance" is a drive subsystem complete with a
small computer that is running some kind of
dedicated server software. Client PCs simply
connect to the device and map drive letters or
volume names to access the data. NASs are a
great way to add capacity to a workgroup without
adding more drives to an already overpacked server
or RAID subsystem. Available from vendors such as
Meridian Data Inc., ProComm Technology, and
Network Appliance, many NAS devices are
relatively inexpensive--starting at as little as
$1,000--and they're a lot easier than a server to
install and maintain.
Other benefits of NAS devices over RAID
subsystems are their openness and scalability.
While you can keep adding drives or subsystems to
your server's RAID controller, you will eventually
either run out of SCSI IDs or break the limit on the
length of the SCSI cable. Likewise, server-attached
RAID subsystems are limited to the protocols and file system formats
supported by the NOS. For example, a RAID system on a Windows NT-based
server can't necessarily store files for your Unix clients. NAS devices support
all of the major protocols and can support most file formats, including NFS,
NTFS, FAT, and HPFS. Also, you can add as many NAS devices as you
want, making their scalability unlimited. Unlike RAID, however, a NAS device
does not provide redundancy.
SAN devices are drive subsystems that are linked directly to one or more
servers via a high-speed Fibre Channel or Gigabit Ethernet connection. The
idea is to house all of your data in a single repository, which can be accessed
by multiple servers and clients. Best for large corporations with disparate
operations that need to interconnect, these storage-centric devices are
currently available from HP, IBM, and other storage vendors. The future of SAN
includes the ability for different platforms such as NetWare, Windows NT, and
Unix to all access the same centralized storage. Unfortunately, different file
formats and protocol issues must be addressed before that becomes a reality.
Another development to watch is the looming battle between SCSI--the
traditional high-speed drive interface--and Fibre Channel. Right now, almost all
drives in servers are SCSI, and it is the preferred way to interconnect RAID
arrays and libraries to the server. Fibre is gaining share as a server-to-server
connection and may begin to usurp SCSI's dominance elsewhere on the chain.
The reason is speed: Fibre delivers throughput of 100 MBps in real-world use,
versus 80 MBps for the latest generation of SCSI (Ultra2 LVD SCSI). SCSI
supporters (such as Adaptec and ATTO Technologies) point out that the next
generation of SCSI, due out this year, will deliver 160 MBps, with a road map
laid out to 640 MBps by 2003. SCSI is also backward-compatible with legacy
devices. Problem is, SCSI is not for long distances where large drive boxes are
connected to multiple computers, and where switches and routers are used.
SCSI is also limited to 15 devices per channel (compared with 128 devices for
Fibre Channel). So Fibre is probably the better choice for large SAN
installations, while the more proven SCSI options might be the right bet (at
least for now) for small and midsize networks.
While the ubiquity and centralized location of SAN and NAS devices is
definitely the wave of the future, you will still depend on the other technologies
in this roundup to implement a complete network storage solution. For
example, just because you centralize all of your server's data into a SAN
device doesn't mean that SAN device shouldn't use RAID. Likewise, SAN and
NAS devices use the same hard disks as any other server, so you need to
back them up to tape on a regular basis. Protecting data online and eliminating
unnecessary downtime is an honorable goal, but for now our motto is still:
Your data is only as good as your last backup. |
