[Ham-Computers] RE: To RAID or not to RAID, that is the question

[Philip Atchley]

Thank you Aaron,

I read the sites you referenced me to (after putting the "ml" in the address 
of the one).  It looks like I'll probably set up the two 80GB drives as 
RAID-1 with the 320GB drive as a data drive.  Before I back up all  my mail 
and other files etc., I have a couple more quick questions.

1.  With the two 80GB drives set as RAID-1, when I go into "My Computer", 
will I see the two drives independently (like Drive C: and D: ) that contain 
the same information (mirrored), or will I see just one drive shown for the 
pair?

2.  When I "install" a program (other than the OS), will it automatically 
know to install to the RAID pair (I assume it would), or how does one insure 
programs are installed correctly?

3.  When the drives are "powered down" under the windows power control, 
(after 30 minutes idle time on this computer) will there be a problem 
"waking them up", or is the automatic power-down a bad idea under RAID. 
Ditto for waking up from Hibernation and/or Standby?

73 de Phil,  KO6BB

See responses in-line...

>>> You wrote:
1.  I now have 3 SATA drives available, two 80GB and a 320GB.  Would I
benefit by re-installing the "extra" 80GB drive and setting up the
drives in a RAID setup?    If so, what "kind" of RAID setup would be
best in this application.  I know absolutely nothing about raid, other
than that my MoBo supports it and that it is a redundant disk system.

>>> My reply:
You have two options...one with a safety margin and one with more drive
space.

a) Configure both 80GB drives in RAID-0 (spanning).  This will allow the
system to see both drives as one large 160GB drive and data throughput
will be faster than just one drive alone.  Contrary to the name, RAID-0
is not redundant - if either drive fails, you've lost the entire volume.
Not a major problem if you do routine backups, but a hassle to
re-install the OS if it does happen.  Make sure to backup often (esp
important data).  This is the "preferred" configuration for apps that
need absolute throughput performance (such as video editing).

b) If 80GB is all you think you'll need for the OS and any applications
you want to use, then configure both 80GB drives in RAID-1 (mirroring).
With RAID-1, the contents of both drives are identical, so if one drive
fails, the system continues to work with the one remaining drive.
Depending on the hardware configuration of the RAID controller, the
RAID-1 set may be slower than the equivalent single drive configuration
(as the controller needs to write to both drives).  Putting both drives
on independent channels (or even seperate controllers) will minimize
this performance hit.  Some higher end controllers manage the drive
writes (via caching) and write to both drives concurrently.

For reference, servers in data centers are often configured with the OS
drive(s) with RAID-1 for fault tolerance.  Some larger "enterprise" data
centers use a "mixed" RAID-1 configuration like RAID-5/1 (A RAID-5 set
mirrored with a second RAID-5 set)...this gets expensive and is
generally only used on "mission critical" servers that can't afford any
down time.  You can even mix RAID 5 and 0 (5/0) to form a spanned RAID-5
set.  Faster than RAID-5 itself and somewhat fault tolerant.


>>> You wrote:
2.  Are the SATA drives "independent" from the EIDE (CD ROM) drives from
a support standpoint?  I know that in a typical EIDE set-up you can only
have 4 drives, 2 master and two secondary.  Does this still apply with
modern technology like SATA?

>>> My reply:
SATA drives are independant with dedicated 1.5Gbps (or 3.0Gbps) data
channels.  They eventually link to a SATA host controller so any
bandwidth limitation will generally be at the host controller or the
drive.  Most drives today still can't max out the 1.5Gbps rate of SATA,
so the drives themselves are the limiting factor.


>>> You wrote:
3.  If I go with RAID, do I need to wipe my disks and start fresh, or
can it be accomplished without having to trash the present files etc.
(XP-Pro using NTFS file system)?

>>> My reply:
Usually, yes, you'll need to re-install the OS.  When configuring RAID,
the controller generally needs to be configured into RAID mode and this
changes the basic Hardware Abstraction Layer (HAL) in Windows.  Windows
is fairly plug-n-pray (oops, plug-n-pLay), but the NT based kernel of
WinXP does't like HAL changes.  Generally, you'll get a BSOD Stop Error
during boot-up.  An exception is if you're not changing the boot drive -
as long as any changes you make to the controller don't affect the
"mode" of the controller Windows boots from, you're fine.  Otherwise, OS
re-install is needed.


>>> You wrote:
4.  Will RAID work with two different disk sizes (two 80GB and one
320GB)?  ALL are Western Digital drives.

>>> My reply:
Maybe.  Some RAID controllers support the "JBOD" mode (Just a Bunch Of
Disks).  JBOD is a spanning mode, so it works like RAID-0.  So, with the
320GB and 80GB drive, you'll get a single volume of 400GB.  I generally
don't like mixing drive sizes in any RAID mode, so I don't recommend
JBOD unless absolutely necessary.


>>> You wrote:
5.  And finally, if RAID isn't the optimum option for me, I can always
either keep the extra 80GB drive as a spare for the one now in
operation, or get a "hot swap" drive bay and use it to "clone" from the
main drive in case it fails in the future.

>>> My reply:
6.  Since both are "matched" drives, so-to-speak (you got them at the
same time, so they should be from the same batch), RAID-1 is a viable
option.  It's more convienent than the drive swap method, but it does
put "hours" on both drives.


>>> You wrote:
What do the guru's out here think my best course of action would be?

>>> My reply:
It'll take a bit longer, but mirror the 80GB drives and use the new
320GB drive as your main "data" drive.  Also, point your paging file to
the 320GB drive as paging to a non-OS drive is more efficient (as long
as it's a "physical" drive and not a different partition on the same
drive).

BTW, if you have 1GB RAM or more, set the paging file to 256/512
(min/max).  Also configure the "DisablePagingExecutive" registry setting
to "0" (zero).  This will prevent Windows from paging any "kernel"
components to the paging file.  I can post the specific keys, if needed.

Just my $0.02.  If you need more details about RAID, here are two good
links:

http://www.storagereview.com/guide2000/ref/hdd/perf/raid/levels/index.ht
ml
http://www.pcguide.com/ref/hdd/perf/raid/index.htm


GL & 73,

  - Aaron Hsu, NN6O


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