I think some clarification of wants
vs needs vs RAID levels is in order.
In our video world there is a need
for massive amounts of storage and speed to deliver that data
to our NLE's: But having large amounts of storage means that
any drive loss can spell doom on your project. So regardless
of what kind of drive/raid/storage solution you decide upon you
MUST have a BACKUP plan that works (and you have tested) in place.
If your needs are just lots of
storage, then I would recommend buying large Firewire drives
and hanging them off your system. Remember to think seriously
about your backup procedures. A dead drive is lost time/data
BUT... If your needs are to greatly
improve Data Transfer Speed and/or you need some protective Redundancy
then you need to consider a RAID array...
is defined as Redundant Array of Independent Drives. Raid arrays
come in 2 forms: Hardware or Software (simulators) For the sake
of this discussion I am only considering hardware Raid controllers
as I would never ever trust a software Raid scenario in my heart
of hearts (sorry software vendors)
There are a variety of RAID levels
(levels of redundancy/performance) Currently IDE/Firewire solutions
seem to only support Raid 0,1,5. SCSI supports 0,1,5, and above.
I have tried to summarize this
in English and techlish:
- If you just want flat out SPEED Raid 0 is the way to go. Lots
of vendors offer this solution.
TECHNICAL: RAID Level 0 provides no redundancy. RAID Level 0 splits
or stripes the data across drives, resulting in higher data throughput.
Since no redundant information is stored, performance is very
good, but the failure of any disk in the array results in complete
data loss. Level 0 is only used to increase disk performance.
- If you want some level of redundancy but cannot afford Raid
5 then go with Raid 1(mirroring) you do not gain any speed but
you do have the advantage of having an instant 2nd copy of your
files. But if you are NOT using some form of backup that works
for your environment then this might be a waste. Since, if you
write bad data out, it is bad in 2 places instantaneously AND
in the very small possibility that the controller goes bad you
will write garbage to both drives thus rendering them both useless...
Again lots of vendors offer this solution.
On our Xserve's we run Raid 1 on
2 drives, and then we use Carbon
Copy Cloner to perform a scheduled clone/rsync/backup every
night to a third drive, we also perform a backup to tape... Apple
does not support R5 on Xserve's, although I see where FWB software
does... I just do not wish to have FWB drivers installed on my
TECHNICAL: RAID Level 1 is usually referred to as mirroring. A
Level 1 array provides redundancy by duplicating all the data
from one drive on a second drive so that if either drive fails,
no data is lost. This is a good entry-level redundant system.
Most newer motherboards have this option built-in today using
the Promise Technology IDE RAID chip. The downside to this is
that the cost per megabyte of disk storage is twice that of a
single drive as two drives are needed to store the same data.
RAID 5 - SPEED, and Redundancy: Raid5 is the way we go
with all critical systems. Our office file servers are all R5.
I have lost single drives in many of these systems at various
times and have NEVER (knock on wood) lost any information. Drives
can be pulled when their indicate they might go bad and replaced
on the fly (w/o stopping the array or usage) and the array re-built.
Depending on the controller (SCSI) you can also tune the read
write characteristics to better suit your READ or WRITE needs...
This can be almost as fast as RAID0 if the right drives and controllers
are used. And provides complete safety of your data. In addition
some controllers (SCSI) support extra spare drives which will
automatically be added to the array in the event of a drive failure
and depending on how many drives are being used you can lose
as many as 2 drives at the same time w/o loss of data. Many people
offer SCSI Raid 5 but it is expensive and you need to choose
a vendor and/or your components (Do It Yourself) with more care...
as controller/OS/software issues can make or break you...
FOR DIY'ers www.infortrend.com
is the OEM that makes many of the actual hardware controller
boards you will find inside the pre packaged manufactured arrays.
For any SCSI Raid Arrays you might purchase I would recommend
Adaptec controllers as they are the ones most likely to be OS
10.3.x >> onward compatible. I personally use a Adaptec
39160 controller in my FCP machine it will allow me to hang as
many as 30 drives off of it..
I did a cursory search for a "relatively"
inexpensive (USD$2-$3000) RAID 5 FIREWIRE solutions for
the Mac and came up with:
They seem to have a 1TB R5 limit...
So currently for arrays larger than 1TB I believe you will need
to go with a Fibre Channel Solution from www.apple.com - Xserve
RAID - 1-3TB (4-14 drives) or a Fibre Channel or SCSI/SERIAL
ATA solution from other aftermarket array makers like:
www.raidinc.com (4-16 drives)
www.medea.com (4-10 drives)
TECHNICAL: RAID Level 5 stripes data at a block level across several
drives and distributes parity among the drives. No single disk
is devoted to parity. This can speed small writes in multiprocessing
systems. Because parity data is distributed on each drive, read
performance tends to be lower than other RAID types.
The actual amount of available
storage is about 75% to 80% of the total storage in the disk
array. The storage penalty for redundancy is only about 20% of
the total storage in the array. If one disk fails it is possible
to rebuild the complete data set so that no data is lost. If
more than one drive fails then all the stored data will be lost.
This gives a fairly low cost per megabyte while still retaining
An easy formula is 4 drives of
120gb == ~360gb of storage. 5 drives of 120gb == 480gb of storage.
you must have minimum of 3 drives in a RAID 5 configuration.
i.e. lose a ~drives worth of space.
For an even more complete course
on hard drives and RAID check out:
RAID levels 6--> 15 if you are looking into this arena write
Jon Golden, is a Virginia based still photographer http://www.jongolden.com
that does some FCP video work, but has a background in Computer
Science, and has consulted IT in the publishing industry for
many years. He has been playing with computers since 1973 and
Mac's since 1987.
copyright © Jon
This article first
appeared on www.kenstone.net and is reprinted here
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