Hardware Reference
In-Depth Information
Video performance
Video performance is of literally zero importance, because we'll run our
home server headless. That is, we'll temporarily install a monitor while we
install and configure Linux, but we'll subsequently manage the server from
a desktop system elsewhere on the network. We'll either use a motherboard
with integrated video, or install a video card for just long enough to get
Linux installed and working.
Disk capacity/performance
Disk capacity and performance are very important. Our home server will
have only one or two simultaneous users, so standard 7,200 RPM SATA
hard drives will provide more than adequate performance. Capacity is the
more important consideration for our server. We want 6 TB of hard disk
space initially, and we'd like to be able to expand that to 12 TB or more with-
out making major changes to the case or the existing drive subsystem. That
means we'll need to use relatively few high-capacity hard drives instead of
many lower-capacity drives.
RAIDforHomeServers
Although we elected not to use RAID on our home server, that doesn't mean
RAID isn't right for your home server.
RAID
is an acronym for
Redundant Array
of Inexpensive Disks
. A RAID stores data on two or more physical hard drives,
thereby reducing the risk of losing data when a drive fails. Some types of RAID
also increase read and/or write performance relative to a single drive.
RAID is NOT Backup
We can't say it often enough. RAID
does not substitute for backing up.
RAID protects against data loss as
a result of a drive failure, and may
increase performance. But RAID does
not and cannot protect against data
loss or corruption caused by viruses,
accidental or malicious deletions,
or catastrophic events such as a fire,
flood, or theft of your server.
Five levels of RAID are formally defined, RAID 1 through RAID 5. (Some manu-
facturers sell proprietary arrays that they describe as RAID 1.5, RAID 5E, RAID
5EE, RAID 6, RAID 7, RAID DP, RAID K, RAID S, RAID Z, and so on, but those are
merely enhanced versions of one of the standard RAID levels.)
RAID levels are optimized to have different strengths, including level of re-
dundancy, optimum file size, random versus sequential read performance,
and random versus sequential write performance. RAID 1 and RAID 5 are com-
monly used in PC servers. RAID 3 is used rarely (generally for streaming video).
RAID 2 and RAID 4 are almost never used. The RAID levels typically used on
home servers are:
Brian Bilbrey Comments
RAID 6 is actually more than just
RAID 5 with another parity stripe. It's
usually configured with a different
checksum algorithm, to protect
against algorithmic weakness. In
addition, with the real possibility of
a bit error during a rebuild following
drive loss, I'd consider RAID 6 to be
required when individual drives of
750 GB or larger are used.
RAID 1
RAID 1 uses two drives that contain exactly the same data. Every time the
system writes to the array, it writes identical data to each drive. If one drive
fails, the data can be read from the surviving drive. Because data must be
written twice, RAID 1 writes are a bit slower than writes to a single drive.
Because data can be read from either drive in a RAID 1, reads are some-
what faster. RAID 1 is also called
mirroring
, if both drives share one control-
ler, or
duplexing
, if each drive has its own controller.
RAID 1 provides very high redundancy, but it is the least efficient of the
RAID levels in terms of hard drive usage. For example, with two 2 TB hard
drives in a RAID 1 array, only 2 TB of total disk space is visible to the sys-
tem. RAID 1 may be implemented with a physical RAID 1 controller or in
software by the operating system.
