[CentOS] Serial ATA hardware raid.

Fri Apr 15 23:48:28 UTC 2005
Bryan J. Smith <b.j.smith at ieee.org>

From:  Franki 
> After abit of searching,
> I found a 4 port 8506 for retail $480 here:

BTW, when I was estimating prices earlier, I was using US$.

> For the record, this machine is to replace a web server with about 60+ 
domains hosted,

I've been maintaining Linux DNS/SMTP servers since just before Apache surfaced, adding CERN httpd and the "patchy."
But the majority of my Linux deployment has been for file servers - especially NFS as of 1999.
I still prefer Fujitsu SPARC/Solaris and, even more so, NetApp filers as NFS/SMB plarforms,
but throwing around TBph is typical.

> some of which get allot of hits,
> most are dynamic 
(Perl/PHP/Java) and the
> server runs local MySQL/PostgreSQL as well.

I feel very strongly about using RAID-0+1 in this configuration if you can afford to reduce your effective storage by 33% over RAID-5.
But the choice is yours.
You're not going to make a massive hit since CPU and network is more important.
But you should still segment network and storage with an AMD8131 HyperTransport tunnel that provides seperate PCI-X channels for each.
And don't skimp on the NIC - get something with at least 256KB SRAM receive cache.

> I don't think speed is as important as redundancy,

RAID-0+1 means you could possibly lose 2 discs and be okay, although there's no guarantee after losing 1.
The other thing 3Ware does is read interleaving between the two mirrors.

> but having said that, for future proofing,
> I'd like to get a good performer as well.

3Ware's ASIC compared to a Microcontroller is like comparing a layer-2 ASIC+SRAM switch to a PC CPU+DRAM that does switching/routing.
The ASIC can do it much faster, although the PC can buffer more.
So it depends if you're just throwing data around like layer-2 switching (switching RAID-0, 1, 0+1 reads/writes),
or if you are calculating dynamic routes in non-real-time (like RAID-5 XORs for parity).
That's why 3Ware calls it a "storage switch."

Of course if you have a 9500, it has DRAM too, so it's like having a layer-3 switch (that can route too).
And without the inefficiency of the PC interconnect.

> Which brings up another question,
> I was looking at populating this thing 
> with 10,000 RPM 8MB cache 40gig (roughly) drives,
> but the only drives I 
see in my pricelists that
> match those specs are Western Digital 
> and I generally have stayed away from WD drives in the 
> past due to dodgy standards implimentation
> and the problems that can cause with Linux,

First, other than Maxtor, Seagate and Hitachi, no one makes their own drives.
WD taps the first and last for many, and Maxtor's approch is different than Seagate and Hitachi (I'll send you a link to any explaination).

Secondly, the ATA drives *never* talk to the system, only the 3Ware ASIC.
And unlike GPL Linux, 3Ware can get proprietary command set info from vendors.
I have *never* had a "DMA timeout" in the history of my 6-year 3Ware  usage.

> should I continue to stay away?

WD's 10,000rpm drives come off the same "enterprise" line as Hitachi's SCSI/SATA.
They are not commodity at all.
Hitachi and Seagate have dedicated "enterprise" lines for some SCSI/SATA,
and then "commodity" lines for SCSI/SATA/ATA.
Maxtor has only one line and then tests for tolerance and those that rate high are then declared "enterprise" with a 3-5 year warranty.

> Actually, now that I think about it,
> I guess 10,000 rpm drives with raid is probably over kill for my usage,

Actually, since you are more concerned with latency in your application,
then a faster spindle is better.
In reality, the higher the density, typically the higher the DTR.
So it is very common to see lower density or 1-gen back of higher spindles have a *lower* DTR than a lower spindle.

> but they are pretty cheap anyway, (149 AUD each) but
> if WD are still dodgy

I have WD 40, 80 and 160 "consumer" ATA/SATA drives that give some chipsets fits under Linux,
but 0 issues on a 3Ware card.

> then I'd probably go for 
7200rpm seagates
> as I can get the 8MB 80gig 7200rpm drives for $85 AUD.

Seagate is the only manufacture giving 3-5 year warranties on their "consumer" drives instead of 1-3.
Yes, they cost 10-20% more than Maxtor/WD, but that's piece-of-mind IMHO.

The "sweet spot" right now seems to be 200GB (160-250GB) for size, density (DTR performance) and price (sub-US$100).
(4) 200GB = 400GB effective RAID-0+1.

> Are Western Digitals still dodgy?

All "integrated drive electronics" (IDE) drives via Advanced Technology (AT) Attachment (ATA) seem to do a poor job of following ATA-5 and ATA-6 specs.
But with 3Ware, I've yet to have an issue.
I even have 80GB WDs on old 3Ware 6000 series cards with 3-year-old firmware 6.9 that don't have an issue.

BTW, 40C is the maximum ambient temperature a "consumer" SCSI/SATA/ATA drive should be exposed to.
Drive life dives off if they run hotter.
So consider getting a hot-swap enlosure that fits in a  3x5.25" bay that has 5 bays.
They run $150.