[plug] SATA & Debian

[Tim Bowden]

On Thu, 2004-01-15 at 01:18, Craig Ringer wrote:
> I'll respond with a few comments, but it's late and I'm tired (can't 
> sleep, as usual). Of course, I'm no expert at the best of times.
> 
> 
> Tim Bowden wrote:
> > 1.  SATA looks like it is no longer a goer.  Thanks for the advice
> > Craig.  If I can get about the same performace from PATA with software
> > raid then that's good enough.
> 
> It's likely that you will; I suspect your bottlenecks are more likely to 
> be the drives or PCI bus than the ATA interface. CPU and memory may also 
> play a big part if you're using software RAID, but I haven't used it 
> enough to really say.
> 

CPU & ram will be enough to handle the load for a while.  The existing
web/ database server (& print & small file server) are running of a slow
P2 with 64mb ram.  It's a bit slow but transfering the web & database to
the new system shouldn't put too much of a load on it.


> > 3.  I realise the lan will be something of a bottleneck but nothing is
> > going to be done about that yet.  Most of the computers on the network
> > are laptops, so the file transfers tend to be copying entire job
> > directories to and from the server (up to 1 gig for the larger jobs but
> > usually less than 50mb).
> 
> A single laptop is often capable of maxing a 10/100 ethernet connection 
> - my laptop's disk is capable of ~16MB/s and it's 4200rpm. That said - 
> it all comes down to how much it /really/ matters. After all, if you 
> wanted to eliminate the network bandwidth bottleneck you'd need:
> 	- a 10/100 core switch with at least one gigabit port
> 	- a gigabit NIC in the server attached to PCI-X, 66/64 PCI, or directly 
> to the southbridge
> 	- seriously fast disk storage, especially if being accessed by multiple 
> clients at the same time. Wouldn't be surprised if you needed at least 4 
> drive RAID5 or RAID10.
> 
> Somehow, I doubt it'll be worth the money.
> 

No, it's not worth the money.  Whilst these things will all make for a
much better system, I have to look at it in comparison to the existing
setup.  Most of the files are being served from a desktop system.  The
biggest benefit will be redundancy with the raid (I know it's not
perfect redundancy) and having a dedicated system that is not spending
its time and resources in combat with MS Office.  It doesn't take much
of a system to beat that, but I would still like to get the best system
possible for 'not much money'.  Like usual, I want something for nothing
which I know I won't get.

> > I am planning on using case fans to
> > maximum effect.
> 
> You'll get at least once pre-installed on a good case. My home Lian Li 
> fulltower has 2x80mm filtered intake fans blowing across the drive cage 
> and two 80mm exhaust fans, in addition to the PSU. As my lounge gets 
> _really_ hot in summer, this is a good idea - and I usually disable the 
> rear exhaust fans for winter.

This will be in airconditioned premises so no heat extremes to worry
about. :-)

> 
>  > is the standard cooling that comes
> > with Intel & AMD box sets good enough for 24*7 operation?
> 
> I've never had an issue with them. After all, AMD and Intel don't want 
> warranty returns due to early failure of a CPU, do they? I suspect the 
> standard coolers only become an issue for overclockers or people 
> installing in apallingly ventilated environments.
> 
> > 5.  While serving files will be the main use of this machine it will
> > also double as an internal web and database server (& perhaps mail). 
> > Eventually this will start to put a significant load on the disks as use
> > and content grows so HDD speed is important.
> 
> It depends a lot on the nature of the load. I have little experience 
> with the load types you're talking about, beyond the initial heavy 
> testing I did before deployment and occasional special conditions (full 
> system network backups, etc) with the big server at work. I have a few 
> ideas but do take them as just that - ideas, and second hand advice.
> 
> If you'll be streaming data from it to clients, doing database access, 
> random access from the web server, /and/ mail, I suspect you are likely 
> to hit performance issues (read latencies on random reads mainly) with 
> any single volume drive setup. Certainly if you're doing all of this 
> fairly heavily. If your mail, DB, and web access is only light or your 
> streaming I/O is relatively infrequent then it may not be such an issue.
> 
> I've found that while our server at work performs fine with one or two 
> heavy read/write streams, as soon as we go above that the performance 
> begins falling significantly. Essentially it looks like the (3 disk) 
> RAID array has to start seeking around serving requests in turn - 
> certainly the total throughput falls significantly with each new I/O 
> stream above two or three. Additionally, if I try any kind of random I/O 
> (say heavy IMAP access from several clients) while doing streaming I/O 
> the random I/O performance can be apalling. My RAID5 write performance 
> is also _very_ poor compared to read performance - I hear that using 4+ 
> disk RAID5 instead of 3 disk helps this issue a lot, though. Because of 
> this, I now keep our mail, databases, etc (/var basically) on the RAID1 
> "OS" volume and the big stuff on a separate RAID5 volume. With that 
> setup, I get a responsive OS, apps, db and mail server even when the 
> RAID5 volume is being thrashed by Production.
> 
> You can go right up to a system with a RAID1 volume for OS, web, DB, and 
> mail plus a 4xRAID5 or RAID10 setup for streaming I/O - but are you ever 
> likely to need it? Will it be worth the money?
> 
> It really depends on when /eventually/ is, how clear an idea you have of 
> your expected loads, whether you will want a hot-spare later, what your 
> budget is now, etc. Perhaps that 2 disk RAID1 7200RPM system will be 
> good enough that it's not worth spending the significantly greater 
> amount of cash on a more "serious" machine. The POST ran well enough on 
> a single 1.2GHz Athlon with an 80GB 7200rpm disk (and good tape backups) 
> for a long time. Our move to all-digital publishing and thin clients 
> ended that one, though, as our storage needs went through the roof as 
> did our CPU and memory requirements on the server.
> 
> > 7.  HDD's.  My preference is for Seagate drives going off my own
> > experience and comments from the list in the past, but if I'm going to
> > go with PATA with 8mb cache then WD JB's are the most economical.  What
> > sort of experiences have people had with the latest Western Digital JB
> > drives?  I know WD went through a patch a while back where you wouldn't
> > want to touch on of their drives but perhaps that was too long ago now
> > (thinking back it may have even been four or five years ago.
> 
> I went through a massive rash of failures in them about a year ago and 
> haven't bought any since. That said, my experience appears not to have 
> been widespread and I may have bought a bad production run.
> 
> My core server at work is very happy running on Seagate Barracuda V 
> drives, and I get great results at home with a pair of Maxtor 120GB 8mb 
> cache drives. Both significantly outperform the single surviving (older) 
> WD JB I still have in my home machine.
> 

I'm going to look into hdd's a bit more.  I've been recommended to stay
away from Maxtor at the moment but that was a sample of 1 (admittedly a
reseller) so more research needed.

Tim Bowden