[nycbug-talk] File Backed Disks- Speed Issues

[Pete Wright]

On Thu, Sep 28, 2006 at 11:30:25PM -0400, David Lawson wrote:
> >
> > Well, erm- I've found the sata systems to be every bit as snappy at
> > this scale- (4 drives per 1u box).
> 
> There shouldn't be much of a noticeable difference, honestly.  SATA  
> bandwidth is 300Mb/s, SCSI is 320Mb/s.  I'm inclined to think that  
> any observed difference in performance would be due to controller  
> scaling issues or something similar, rather than the actual  
> throughput on the devices.  This changes when you compare SATA and  
> SAS (Serial Attached SCSI), where there's an order of magnitude  
> bandwidth difference between the two.  I just noticed that Dell has  
> started selling SAS drives and there appear to be quite a few hitting  
> the market lately, I've got a pretty large server order in for boxes  
> with them, so we'll see how they do.
> 


It's not the throughput of the SATA bus that is a limiting factor
(atleast with sizeable datasets with streaming I/O patterns...i.e.
playing back high rez video in realtime) it's the speed at with SATA drives 
spin at that can become the bottle neck.  For a NAS's and other things
you also have to look out for the latency read/write times on SATA
disks, which to be honest I have not looked at closely in a while.

We have actually done some hardware/partioning hacks to get SATA
drives to throughput data close to SCSI speeds...but there are definatly
caveat's when going this route.

for general purpose serving I think SATA stuff is OK for most uses,
although for "enterprise" storage I would not trust it beyond
tier-2/desktop purposes.

-p

-- 
~~oO00Oo~~
Peter Wright
pete at nomadlogic.org
www.nomadlogic.org/~pete
310.869.9459