Hardware Reference
In-Depth Information
Strength in Numbers
One of the advantages of having several hard drives installed is
that it provides a great deal of flexibility. With three 2 TB drives,
for example, you can configure your disk subsystem as a 6 TB
JBOD or a 4 TB RAID 5. With four 2 TB drives, you can set up an 8
TB JBOD, a 6 TB RAID 5, or a 4 TB RAID 10.
network was the bottleneck. Network file reads and writes were
no faster with RAID 10 than with JBOD, again as we expected.
We concluded that using RAID with 7,200 RPM drives in the
server was pointless. But, although we didn't have enough
5,400 or 5,900 RPM drives to test our hypothesis, we would
expect a server using those slower drives in a JBOD to be disk-
bound rather than network-bound. In that case, we'd probably
buy an extra drive or drives and configure them as a RAID 10.
When 10000BaseT network components become affordable,
we'll revisit the RAID issue.
We actually borrowed a fourth 2 TB Barracuda XT from one
of the other project systems long enough to test a RAID 10
configuration. When we tested hard drive performance locally,
RAID 5 and particularly RAID 10 were faster than JBOD in some
benchmarks, as we expected. But for accessing files over the
network—which is all that really matters—our 1000BaseT
Of course, you needn't fill all or even most of your drive bays initially. You can
start small and expand as needed. For example, you might start with just one
or two drives, and simply add another drive each time your data approaches
maximum disk capacity. This is particularly easy to do with a JBOD; with a RAID
you may have some backing up and restoring and reconfiguring to do each
time you install a new drive or drives.
Ad Hoc Backups
Don't overlook the opportunity to use new drives for ad hoc
backups when you expand your system. For example, one of
our readers started with a pair of 7,200 RPM 1 TB drives set up
as a RAID 1. Then she got into shooting HD video and decided
to add a pair of 5400 RPM 1.5 TB drives for bulk data storage
and to convert the RAID 1 to a JBOD to give her additional fast
hard drive capacity.
That took her from a 1 TB RAID 1 configuration to a 5 TB JBOD,
and of course she ran two full backups to eSATA external hard
drives before doing anything else. Then she realized she could
use the two new hard drives to make two more full backups. So
she put the two new hard drives in her eSATA dock, formatted
them, copied the contents of the RAID 1 to both of them, shut
down the system, and disconnected the drives.
She said she'd have been very uncomfortable having only one
full backup before breaking and reformatting the RAID 1, and
at least slightly uncomfortable having only two backups. But,
as she said, with four full backups there was more chance that
she'd be struck by lightning than that she'd lose all her data
during the upgrade.
The Big 3-0
As we wrote this, 2 TB drives were the largest available, but
Seagate has announced plans to ship a 3 TB model in late 2010.
No doubt Samsung, Western Digital, and other drive makers
will follow Seagate's lead and introduce similar models.
Unfortunately, the BIOSs on nearly all current motherboards do
not support booting from drives larger than 2 TB. This is a hard
limitation. There's no way to get around it, short of replacing
the motherboard with a model that uses a
Unified Extensible
Firmware Interface
(UEFI) BIOS.
Fortunately, this limitation applies only to the boot drive. As
long as you boot the system from a 2 TB or smaller drive, and
as long as your operating system, HDD device drivers, and/or
HBAs or RAID controllers support drives larger than 2 TB, you
can install as many 3 TB drives as you have SATA ports available
for them.
With three 2 TB drives and five spare drive bays, we have room
to expand our own server to a total of 21 TB without replacing
any drives. That should suffice for the expected life of the server.
