[asterisk-users] New system for recording - SCSI, SAS or SATA?

[Tony Mountifield]

In article <m3skjpgfvb.fsf at ursa.amorsen.dk>,
Benny Amorsen <benny+usenet at amorsen.dk> wrote:
> tony at softins.clara.co.uk (Tony Mountifield) writes:
> 
> > I'm in the process of specifying the hardware for some new Asterisk
> > systems which will be running a substantial number of conferences
> > with recording.
> >
> > I was wondering what there is to choose between SCSI, SAS and SATA
> > disks, in terms of performance for this kind of application.
> 
> Modern SCSI, SAS, or SATA drives don't perform differently because of
> the interface type. You can't get 15kRPM SATA drives because the market
> for those is too small though.
> 
> If you record 1 channel in Alaw, you need 2 x 64kbps disk bandwidth, or
> 16kB/s. If you record 1000 channels, you need 16MB/s from your disks,
> which should be easily achievable with even the cheapest disks. However,
> that depends on doing sequential writes. You can only do (best case) 120
> random writes pr second on a 7200RPM disk without write cache, and you
> can reach that limit with just 2 channels, if you have to do a seek pr
> packet. The solution there is write cache; 1 second gives you 120
> channels and 5 seconds bring you up to 600 channels.
> 
> If you are unlucky and the files are placed widely spaced on the drives,
> the performance will be lower than those numbers.
> 
> So, to get decent performance from many streams, you need a lot of disk
> write cache, either on the disk itself (with the risk that a power failure
> destroys data), on the controller, or in memory. You can gain a factor
> of 2 by going to 15kRPM disks, and another factor of two by doubling the
> number of spindles (if you get the layout right). The Linux write cache
> can be tweaked for this purpose, but again you risk that a power failure
> destroys data.

Benny, thanks for the info - useful things to consider. Sounds like disk
speed and cache are the critical factors, rather than their interface.
I'm not too worried about power failure; the units will have redundant PSUs
and will be in an environment where the power is reliable.

Cheers
Tony
-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org