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RAID setup help

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September 24, 2004 3:17:09 AM

Archived from groups: alt.comp.hardware.homebuilt (More info?)

Hi

First of all, what is the difference between a RAID controller and a RAID
card. Promise (www.promise.com) seem to have two product ranges of the above
products.

And also, what is the best RAID controller/card (not just promise) to go
for, that won't slow the performace of my PC in any way, when 4 drives are
connected to the controller?

Thanks

More about : raid setup

Anonymous
a b B Homebuilt system
October 2, 2004 10:43:55 PM

Archived from groups: alt.comp.hardware.homebuilt (More info?)

Phil wrote:

> First of all, what is the difference between a RAID controller and a RAID
> card. Promise (www.promise.com) seem to have two product ranges of the
> above products.
>
> And also, what is the best RAID controller/card (not just promise) to go
> for, that won't slow the performace of my PC in any way, when 4 drives are
> connected to the controller?

You must be referring to a SATA controller vs. a RAID controller. They list
a 'Serial and ATA RAID Card' and a 'Serial and ATA Controller'.

Normal desktop systems shouldn't need anything more than either RAID 0, 1,
or 0+1. Those are very simple systems that only requires a BIOS that can
accomplish the given tasks associated with these simplistic forms of RAID.


Then there are the high-end cards that allow more complex RAID setups like
RAID 5. They usually have onboard processing of their own because they deal
with so much more than a RAID 0 setup would. Therefore, to reduce CPU
utilization and increase throughput, they have their own processing. You
don't need to spend this kind of money. A good RAID 0 setup for speed and a
nice, big external backup HDD will be plenty.
October 4, 2004 2:17:22 AM

Archived from groups: alt.comp.hardware.homebuilt (More info?)

One is a raid card, the other is just a Sata card....with no raid.

"Phil" <phil@nospamjencom.co.uk> wrote in message
news:VPI4d.72406$U04.63935@fe1.news.blueyonder.co.uk...
> Hi
>
> First of all, what is the difference between a RAID controller and a RAID
> card. Promise (www.promise.com) seem to have two product ranges of the
> above
> products.
>
> And also, what is the best RAID controller/card (not just promise) to go
> for, that won't slow the performace of my PC in any way, when 4 drives are
> connected to the controller?
>
> Thanks
>
Related resources
Anonymous
a b B Homebuilt system
October 9, 2004 9:56:20 PM

Archived from groups: alt.comp.hardware.homebuilt (More info?)

Phil wrote:

> First of all, what is the difference between a RAID controller and a RAID
> card. Promise (www.promise.com) seem to have two product ranges of the
> above products.

A card contains a controller, but Promise also makes controllers that are
embedded in motherboard chipsets.


> And also, what is the best RAID controller/card (not just promise) to go
> for, that won't slow the performace of my PC in any way, when 4 drives are
> connected to the controller?

For that you will have to go to SCSI. The reason is that PCI/ATA controllers
use the CPU for much of the I/O work. SCSI cards offload much of that work to
the SCSI controller.

Also, you will have to decide what RAID level you want to use, and how important
performance vs data safety is to you. IMO, RAID 5 is the best compromise for a
4-drive system, because you can get automatic rebuild from any single failed HD,
as well as a significant performance boost.
Anonymous
a b B Homebuilt system
October 10, 2004 3:10:17 AM

Archived from groups: alt.comp.hardware.homebuilt (More info?)

> For that you will have to go to SCSI. The reason is that PCI/ATA controllers use the
> CPU for much of the I/O work. SCSI cards offload much of that work to the SCSI
> controller.

No 3ware cards use decent onboard CPUs (as do Mylex, formerly part of IBM
but a better part than Lexmark became, and so do a few other brands out there).

o SCSI is best for multi-user RAID environments
---- or where you plan on a very large number of drives
---- or where you emphatically need 15.3k-rpm drives re latency
o SATA/ATA are best for single-user RAID environments
---- or where you need lower TCO re lower drive purchase cost
---- or where you need redundancy of that drive array (ie, 2 distributed machines etc)

The reason is relatively simple:
o SATA drive like a WD Raptor 10k-rpm has a *very* high SDTR capability
---- it's seek time (electromechanical latency) is good, but not the world's fastest
o SATA drives however in the present Drive/Card/OS chain lack NCQ/TCQ
---- NCQ/TCQ is where seeks & access are ordered to minimise head movement
---- SDTR means nothing if the heads are seeking all over the place
---- and HD are slow *electromechanical* devices when it comes to head seeking
o SCSI drives conversely often have a lower SDTR than say a WD Raptor 10k-rpm
---- they have very fast track access times - so low electromechanical latency
---- they have SCSI NCQ/TCQ to re-order seeks/accesses - so low electromechanical
latency
o SCSI drives thus perform best in multi-user environments
---- because in multi-user the stress is not SDTR - but in I/O per second (IOPS)
---- if 50 users are accessing a dbase, the peak SDTR means little - seek times do
---- seek times are lower for SCSI drives & lower since SCSI supports NCQ/TCQ

The latest SATA drives do indeed support NCQ/TCQ - but the Card/Drivers do not,
and the O/S does not as yet. You should see a 10-15% improvement when they do,
and another benefit of SCSI is gone (except for 15.3k-rpm drives having a lower
rotational latency than the present 10k-rpm WD Raptor drives of course - at a price).

There are thus 3 "levels" of RAID:
o Cheap-as-Chips ATA/SATA -- s/w RAID or cheap RAID cards with a BIOS
---- Highpoint, some Promise & most onboard RAID fall into the latter category
---- something like a plug-in Intel RAID adapter doesn't (it has an i960 CPU on it)
o High quality & price ATA/SATA/SCSI - true h/w RAID solutions with onboard CPU
---- Promise do one (FastTrak), 3ware do some up to 8/12 devices, Mylex & Adaptec also
---- SCSI ones cost disproportionately more - the Promise/3ware SATA 4-port are good
o External Fibre Channel RAID solutions - despite the price, often use SATA drives!
---- here it comes down to whether server IOPS matters (SCSI) or cost of data-size
matters (SATA)
---- various i/f's (not just FC) can be used, basically O/S independent external
RAID/NAS/SAN
---- for example, a data-warehousing or near-line storage (pre-tape) uses SATA RAID
---- conversely, a e-commerce transaction server uses SCSI RAID, clustering etc

I tend to prefer RAID-10 if you have 4 drives - it is both Mirror & Striping.
It has less overhead than RAID-5, and offers good reliability as well.

It's unfortunate 3ware keep their 4-port card ~3x the price of their 2-port version,
although Promise do a good 4-port card. If you RAID a lot of drives, you need to
think about the bottleneck of PCI - more an issue if doing RAID for SDTR. Most
servers actually don't get particularly high SDTR from their SCSI disks since they
are in a multi-user environment, so access-latency eats into the peak figures. That
is particularly true when loading say user-profiles or handling MS-IE temp files etc.

So RAID for a MPEG production server would be 3ware & WD Raptor x4 - since that
is stressing SDTR of a single-user large-dataset, RAID for a major dynamic-dbase
server would go with a SCSI solution since that stresses lots of file accessing/updating
and as much memory as you can stuff in the thing (where Opteron 64-bit eats Xeon).

RAID is not a backup device - it's about availability:
o Cheap "h/w" RAID cards do *not* offer automatic rebuild on drive-replacement
---- you *must* know how to rebuild that array before it happens
---- it can be quite involved and a mistake could cost you data
o Real "h/w" RAID cards do offer automatic rebuild on drive-replacement
---- be it SCSI or ATA/SATA, from 3ware to Adaptec - but at a higher price
---- note some require the RAID config to be stored on a disk - don't lose it :-)

Hard-drives are electromechanical components and thus can suffer failure from such,
and also from heat - often overlooked re case ambient temps or S.M.A.R.T. drive diags.

Windows can RAID disks - but only dynamic disks (which the system disk can not be :-)

If it's just for reliability on a SOHO system, I'd perhaps choose a mid-way option:
o Non-RAID the system disk
o RAID two data-disks with a 3-ware 2-port card (120$/£100) - RAID-1 mirror
---- auto-rebuild, reliable proven card

If it for reliability with performance, I'd choose a higher-end but cheap option:
o RAID-10 all 4 disks (eg, 2 system & 2 data)
o Use a Promise 4-port RAID card as a good bit cheaper than a 3ware option

If it's a commercial environment then 3ware is a good solution - but expensive >2-port.
The cheap RAID cards have a long google history of "help!" if you search around.
--
Dorothy Bradbury
www.dorothybradbury.co.uk for Panaflo fans (free shipping)
!