RAID choices

[Rene]

Hi,

I'm looking to boost performance with RAID, and I'm wondering which
alternative to consider.

My setup & priorities:
I'm a free-lance SW developer working from my home PC;
Currently configured with 2 physical drives:
C:/ for system
D:/ all user data, DB, swap file
I back-up regularly, and can live with down time in case of hardware
failure; my priority is performance gain;

Currently, I am considering:
3-way hardware RAID0 with IDE drives, then partition the resulting
stripe-set as drives C: and D:
Specific hardware I've seen includes: Adaptec ATA RAID 1200, and Dawicontrol
DC-100

Questions:
1- Given that RAID0 is usually recommended for 'fast/temporary' data, and
not for boot partitions, am I looking for trouble? I do take regular
backups of both C: and D: and could live with the time it would take to
restore in the event of a failure in any of the drives. So are there gotchas
in my approach that I haven't seen?

2-How do I transition from my current HW to the new setup? I assume setting
up the RAID0 will blank out the disks, right? If that's the case, can I
simply 'Ghost' back images of my C: and D: drives after the stripe sets have
been created?

3-Am I right in assuming that in the event of a drive failure, I replace the
failed drive, ghost back or restore from the last backup, then I'm back in
business?

Thanx a million!

René
Montreal

 

[Wichetael]

Hi there,

0. Firstly, if you're really looking for performance gain, check for a
decent RAID controller, the Adaptec 1200 for instance is only a software
RAID controller, ie your RAID is controlled from software and not from
hardware, which basically means crappy performance compared to a real
hardware controlled RAID array. Secondly if you're really interested in
performance look into SCSI drives, many people whine and moan about how
their great IDE drives are (in a very limited number of cases) faster than
the SCSI drives, but people fail to see that lineair sequential throughput
is completely useless in real world applications, what you need is fast
random access which SCSI, with it's ultra low access times can give you,
especially if you go for something like a Atlas 15K IV or Cheetah 15K.6
drive, yes it will cost three times as much as an IDE drive, but it will
give you truly good and reliable speeds, the drive is reliable and will last
you a lifetime and you can be much more confident that you won't be
experiencing any crashes due to harddrive failure. But enough of my
rambling, whatever you choose is ultimately your choice, do at least
consider getting a hardware RAID, a software RAID card won't do you much
good. The catch is of course that hardware controlled RAID arrays are
usually three to four times more expensive than software controlled RAID
arrays, but hey what do you want, you can't expect to be sitting front row
for a dime...

1. Generally RAIDs work very well for system partitions, I myself have used
a RAID setup on two systems and many people I know are happily working with
either IDE or SCSI RAID systems without any troubles they wouldn't have had
in single disk setups.

2. This really depends on your whole setup, but the best approach will
probably be to just get your data safe, ie write it to cds or something or
simply don't use your current data disc in the RAID setup. Then install the
system anew on the RAID config and copy your data to it. Yes, if the setup
were to give you problems you should simply be able to copy your backup
images right back and work with your old setup again. Do keep in mind that
you need to use 100% identical discs in a RAID setup, even if they are just
a tad different, in some cases even different firmware versions can matter,
you usually might as well do away with the whole RAID setup due to
synchronization problems, wait states and other such timing issues. Also the
installation on your RAID setup will be significantly different from the
installation on your current setup as the boot volume will use a different
controller and thus a different driver.

3. No you can't, at least it depends on your RAID controller and most
controller don't support this kind of use, the problem is that along with
the actual data, the RAID system keeps administration information on the
discs which might become corrupted or out of sync with the actual data due
to the restoration of the backup. You can restore a partition image back
into a partition in the actual RAID config, but you can't just restore one
of the physical discs to an older state without also bringing the other
discs to the state of the EXACT same time, and even then it can give you
problems if the RAID controller itself keeps administration data, which some
do.

Anyway, don't be afraid to start experimenting with RAID, it really isn't as
scary as it may sound, at least not when you know what you are getting, what
you need to look for and what you are doing.

Good luck,

Wichetael.

 

[Rene]

Hello and thanks for your reply Wichetael!

I am indeed more interested in HW RAID than software emulation. I'm
surprised to hear that the Adaptec card is a SW implementation. I'm not
sure I understand at this point. I had figured that since it is a card, it
carried the benefit of not burdenning the CPU with RAID related work, and
thus might be classified as HW raid as opposed to a SW raid. Maybe if you
gave me an example of manufacturer/model of a 'true' hardware RAID (SCSI or
IDE) I could look it up and better understand the point you are making.

Thanx again for your reply!

René

 

[Wichetael]

The Adaptec 2400 card for instance is a hardware based RAID controller,
notice the line "The Adaptec ATA RAID 2400A card is a microprocessor-based
RAID solution..." in the product overview, also a true hardware controller
will always need on-board cache to carry out efficient I/O operations.
Though I have not heard many good things about the Adaptec ATA controllers,
despite their excellent SCSI controllers, you might want to take a look at
some of 3ware's controllers such as the 7506-4LP or the 8506-4LP in case of
S-ATA.

Regards, Wichetael.

 

[Doo Wopper]

Hello and thanks for your reply Wichetael!

I am indeed more interested in HW RAID than software emulation. I'm
surprised to hear that the Adaptec card is a SW implementation. I'm not
sure I understand at this point. I had figured that since it is a card, it
carried the benefit of not burdenning the CPU with RAID related work, and
thus might be classified as HW raid as opposed to a SW raid. Maybe if you
gave me an example of manufacturer/model of a 'true' hardware RAID (SCSI or
IDE) I could look it up and better understand the point you are making.

Thanx again for your reply!

René

For performance, You need to use RAID-0 or possibly RAID-10. I have
seen impressive speed performance using RAID0 and the built-in RAID
controller (Promise) on my motherboards (ASUS and Soyo). Generally, the
performace will be almost 2x the single drive speed with a good
controller. However, there is an issue with RAID-0 which is that if
either of the two drives craps out, then you will have lost EVERYTHING
on both drives.

I recommend that if you are going to do this, that you maintain a very
active backup schedule.

For me, I have RAID-0 for my C: (system) and a temp drive (for when I
am video editing). This drive consists of 2-IBM 60gb drives.

Then I also have a 3WARE 7506 RAID controller which I use in a RAID-5
configuration with 4x80gb Maxtor drives. Performace sucks but it is
reliable and if any one of the drives gives out, I have some time to
replace the bad drive. Because of the slow performance, I use RAID5 for
long term storage items.

BTW, I used to think that a good hardware controller with its own
microprocessor was the way to go too. That is why I bought the 3WARE
7506 but I discovered that this is certainly no panacea. Think about it.
A software RAID controller board (not the true XP software) uses the
same processor as the XP OS, ie your CPU. The hardware RAID controller
uses its own processor. So you would think the hardware board will be
faster since it is not loading down your CPU. This may be true in a
multi-user server environment but if you are using this in a personal
computer where you are the only user, you will probably not notice any
performance gain by using the hardware solution. In fact the software
based RAID board may give you better overall performance. The reason is
simple: By using your CPU, which is probably over 1GHz, to do the RAID
provcessing, the software RAID can execute fater than the hardware based
microprocessor which is probably running at no more than 100MHz, if
that. ANd since you are the only user on the system, when you request a
file, you are going to wait until that file is available to you anyway
so it makes no difference which processor is doing what. In fact on the
software based solution, this has the faster processor (your CPU) than a
hardware solution.

And using RAID5, the situation gets even worse because the RAID
calculations are for more stringent than RAID0.

Hoep this helped.

 

[Wichetael]

The speed of the processor has absolutely nothing to do with it, the
limiting factor is the bandwidth of the PCI bus, which will be the
bottleneck in any case, would you really believe that they stuck with
low-speed processors if it would be the bottle-neck in the setup... Besides
that it is not merely the speed of a processor which counts, but it's
bandwidth, and considering that it will be much more rewardable to get a
card with a 64bit PCI interface, but then of course you also need a
motherboard featuring a 64bit PCI slot to take advantage of that bandwidth.

The reason you want your disk I/O happening off board is that you don't want
your CPU being tied up doing simple data moving tasks when it can do
powerful calculations instead. But yes it matters heavily what kind of
things you use, but in my experience, being a software developer myself I
really want to have as much as possible done by hardware, I've got a SCSI
raid, decent NICs and a decent sound card which don't take much CPU power
and system resources. The biggest problem in a software RAID setup is moving
data, if it runs by software all the data will have to pass over the PCI bus
and thus taking away bandwidth from other important tasks, consuming system
memory, requiring administration by the CPU and limiting the CPU in it's
operation by tying up the bus and memory controllers. With a true hardware
based card you can do this completely off the main system handled by just
the RAID board itself. So yes, when dealing with multi-user environment with
on the fly data movement and such, this is not just a good idea, but a
necessity. Though if you're like me and have a multitude of different
programs running at the same time, such as compilers, text processing
applications, graphics editing and manipulation applications, rendering
applications, analysis applications, simulations and debuggers while also
having open numerous browser windows, playing music and having instant
messaging programs active you definately don't want your processor burdened
by such mundane tasks as data moving...

As to the performance of a software controlled RAID 0 array, this
performance you are talking about is only lineair sequential throughput,
which in real world applicatiosn is as useless as the power ratings on
speakers...

Regards, Wichetael.

 

[Frank]

Hi,
I'm looking to boost performance with RAID, and I'm wondering which
alternative to consider.
My setup & priorities:
I'm a free-lance SW developer working from my home PC;
Currently configured with 2 physical drives:
C:/ for system
D:/ all user data, DB, swap file
I back-up regularly, and can live with down time in case of hardware
failure; my priority is performance gain;
Currently, I am considering:
3-way hardware RAID0 with IDE drives, then partition the resulting
stripe-set as drives C: and D:
Specific hardware I've seen includes: Adaptec ATA RAID 1200, and Dawicontrol
DC-100
Questions:
1- Given that RAID0 is usually recommended for 'fast/temporary' data, and
not for boot partitions, am I looking for trouble? I do take regular
backups of both C: and D: and could live with the time it would take to
restore in the event of a failure in any of the drives. So are there gotchas
in my approach that I haven't seen?

2-How do I transition from my current HW to the new setup? I assume setting
up the RAID0 will blank out the disks, right? If that's the case, can I
simply 'Ghost' back images of my C: and D: drives after the stripe sets have
been created?

3-Am I right in assuming that in the event of a drive failure, I replace the
failed drive, ghost back or restore from the last backup, then I'm back in
business?

This RAID situation is like anything else in this world, (if you want to
dance
you have to pay the fiddler).
I have a setup where I use a Fasttrak tx4000. I only use 3 drives in a
striped
mode. The performance increase is perceivable to the eye. I also use an
external
USB HDD enclosure for backing up using Drive Image. I don't use partitions
because it has been my experience that if I lost one partition I would
usually
lose the use of them all. -READ READ READ --- SHOP SHOP SHOP- to fit
your own preferences.