Opinions about fast hard drive vs. raid for OS

[Jeff]

I'm about to order some parts for a new machine and have decided on most items other than
the hard drives. I'm going to put in a Raid 5 with 3 or 4 500 to 750 gig Sata drives for video and
still photo storage (with an AMD FX62 based system), and I'm wondering about whether to consider a separate smaller but faster drive
for the operating system and other files. My current machine runs 2 15K RPM scsi drives
for the OS and frequently accessed files (other than video and .jpgs) with the pagefile split between them, while my
video and other large files are on 200 and 100 gig drives (but not in raid). In the new machine, I'm wanting the
raid primarily for fault-tolerance, but it would also come in handy for speed when doing video editing.

My current machine is just too noisy with the 15K scsis. I want a much quieter machine, so I'll likely not use them,
but instead keep them in the older machine, that I'll use as a spare.
The large drives will be sata, and if I get a smaller drive for the OS, it will likely be sata also, although if it would really
be a benefit for my usage, I might consider a SAS drive. From what I gather,
the smaller Sata drives do come in 10K RPM, although the larger storage drives are 7200.

So - I'm looking for opinions about whether or not to consider a separate higher rpm drive for the OS and more frequently accesses
files, or whether to just make a separate partition on the raid array for the OS. I'm new to raid, so perhaps this is a stupid
question - don't know. I realize that for small tranfers (like that accessing various files for the OS), a high RPM drive with a
rapid burst rate is best, but I don't know whether the high RPM smaller drive will still be slower than 3 or more drives sending out
that same info at the same time. Backup is also a consideration, as I'll likely back up everything but the OS and programs.

Jeff

 

[hdrdtd]

In my servers at work, i usually configure two HD's in a RAID 1 (mirror) for
the OS and programs. I'll also configure a RAID 5 array for data storage.

It all depends on your 'need for speed' and budget if you use high-speed
SCSI drives or not.

either way, i'd reccomend using a good add-in RAID adapter rather than any
RAID features that come built-in on the motherboard.

an add-in RAID card will probably have a much richer set of features than
any built-in solution.

 

[Jeff]

Again, a question from someone new to RAID - does one need two RAID adapters/cards if you run a set-up similar to what you're
describing where you have a RAID 1 and a raid 5? Also, I'm assuming that a Raid 5 can be partitioned just like if it was a single
drive? ...and if the MB says that it handles RAID, does this mean software RAID, or hardware raid?

Thanks in advance

Jeff

 

[HDRDTD]

It all depends on the RAID controller. Many SCSI RAID controller are at
least dual channel, meaning there are two or more SCSI channels(connectors)
and you can have sepearate independant RAID configurations.

Yes a RAID 5 can be partitions just like a single drive. The OS doesn't know
the difference.

IF the MB says it handles RAID, then yes it's a hardware RAID.

 

[Jeff]

Thanks

It all depends on the RAID controller. Many SCSI RAID controller are at
least dual channel, meaning there are two or more SCSI channels(connectors)
and you can have sepearate independant RAID configurations.

Yes a RAID 5 can be partitions just like a single drive. The OS doesn't know
the difference.

IF the MB says it handles RAID, then yes it's a hardware RAID.

 

[John Weiss]

If you have a 32-bit PCI bus for all that RAID, your performance is not
going to be stellar, because of the inherent PCI bus bandwidth limitation of
133 MBps. On-board RAID or a 64-bit PCI add-in or possibly PCI-e will allow
higher inherent performance.

A pair of 10K RPM Raptors will take care of the OS and pagefile handily.

 

[Jeff]

I've just ordered the Gigabyte GA-M59SLI-S5 Motherboard (AM2 for an FX-62). I also ordered one of the 10K Raptors.
....will probably take a few weeks to get everything in and assembled as I'm not in that big of a hurry.
The MB has plenty of PCI-e slots, and I'll probably only use one for a dual DVI video card. I think that what I might work toward is
a pair of raptors in raid 0 for the OS as you suggested (and I've found similar info elsewhere), pagefile, and programs, (that I
won't bother backing up - or will do so only infrequently by making a clone to an older drive) and then a second raid 5 for the
video and other large files. I assume that the MB will only handle one of the raid combinations, so I'll need a separate controller
for the second? In quickly looking at Promise's site, I see that they have PCI-e cards as well as slower ones. Do I understand
correctly that you are suggesting that buying a PCI-e one is worth the cost?

Jeff

 

[HDRDTD]

Absolutely

I've just ordered the Gigabyte GA-M59SLI-S5 Motherboard (AM2 for an
FX-62). I also ordered one of the 10K Raptors.
...will probably take a few weeks to get everything in and assembled as
I'm not in that big of a hurry.
The MB has plenty of PCI-e slots, and I'll probably only use one for a
dual DVI video card. I think that what I might work toward is
a pair of raptors in raid 0 for the OS as you suggested (and I've found
similar info elsewhere), pagefile, and programs, (that I
won't bother backing up - or will do so only infrequently by making a
clone to an older drive) and then a second raid 5 for the
video and other large files. I assume that the MB will only handle one of
the raid combinations, so I'll need a separate controller
for the second? In quickly looking at Promise's site, I see that they
have PCI-e cards as well as slower ones. Do I understand
correctly that you are suggesting that buying a PCI-e one is worth the
cost?

Jeff

 

[John Weiss]

I assume that the MB will only handle one of the raid combinations, so
I'll need a separate controller for the second? In quickly looking at
Promise's site, I see that they have PCI-e cards as well as slower ones.
Do I understand correctly that you are suggesting that buying a PCI-e one
is worth the cost?

"Worth the cost" is up to you.

A 4-HD RAID 5 array that is capable of 320 MBPS+ (assuming 80 MBPS nominal
per HD) will be choked by a 133 MBPS PCI bus. If you're going to spend $$
for 4 fast drives, the $$ spent on a card on a fast bus will be well spent.

You may want to go to Tom's Hardware or similar site to find out what a
particular card/HD combination may do on benchmarks...

 

[Jeff]

A 4-HD RAID 5 array that is capable of 320 MBPS+ (assuming 80 MBPS nominal
per HD) will be choked by a 133 MBPS PCI bus. If you're going to spend $$
for 4 fast drives, the $$ spent on a card on a fast bus will be well spent.

You may want to go to Tom's Hardware or similar site to find out what a
particular card/HD combination may do on benchmarks...

Your explanations are very helpful. I follow most of the example above, but I'm not sure about one thing. Where does the 133 MBPS
PCI bus figure come from? I know a good bit about harddrives, enough to get by on processors and ram, but I know almost nothing
about bus speeds. I've looked through the specs on the MB, but can't find anything that explains about bus speeds. I'm not sure that
I understand why a controller integral to the MB would run slower than an add-in card. Is this a quick explanation that you can
give, or can you point me to a site that could explain this in more detail? I don't mind reading, but I'm not always certain where
to go for good information.

Jeff

 

[John Weiss]

Your explanations are very helpful. I follow most of the example above,
but I'm not sure about one thing. Where does the 133 MBPS PCI bus figure
come from?

33 MHz * 32 bits wide / 8 bits per byte

I'm not sure that I understand why a controller integral to the MB would
run slower than an add-in card. Is this a quick explanation that you can
give, or can you point me to a site that could explain this in more
detail? I don't mind reading, but I'm not always certain where to go for
good information.

The point is the add-in 32-bit PCI card will run slower than most on-board
controllers. I don't know where you got the impression that the opposite
was true.

You asked about putting 1 array on the MoBo controller and the second array
on an add-in card. That second array is the one you have to worry about.

 

[Jeff]

The point is the add-in 32-bit PCI card will run slower than most on-board
controllers. I don't know where you got the impression that the opposite
was true.

You asked about putting 1 array on the MoBo controller and the second array
on an add-in card. That second array is the one you have to worry about.

Thanks. I got the wrong impression from misreading something you wrote previously. I went back and read it again and I now see my
mistake. Your original wording was correct - my mistake.

Thanks for putting up with the questions.

Jeff