Re: SATA performace

[Konstantin Olchanski <olchansk@triumf.ca>]

On Mon, Jan 02, 2006 at 11:47:59PM -0500, Ross Vandegrift wrote:
> On Mon, Jan 02, 2006 at 10:43:47PM -0500, Paul Aviles wrote:
> > Are SATA drives similar in performance than IDE drives? I have tested 
> > Barracudas 7200.0 (500Gb) and WD too on the same type of servers (more than 
> > 1 unit) and what I am getting is painfully slow in terms of read/writes. 

In modern systems, disk performance is dominated by the physical disk
characteristics: rotation speed and seek times (ignoring speedups from
Linux-level, controller-level and disk-level i/o reordering and caching).

So you should (and we do) see almost identical performance between
similar PATA and SATA disks. For bulk data streaming, you should see
30-60 Mbytes/sec for a single disk.

The only performance-degrading problems I have seen are a) PATA
disks running in non-DMA modes (bulk data streaming rate = 3 Mbytes/sec)
and b) barely-readable sectors on many new high-density disks (disk-level
read retries, takes seconds to read one sector, kills performance).

Problem (b) is quite evil and hard to diagnose: it seems to be temperature
dependant, it is not reported by SMART, and it is not reported
by Linux (unless it is so bad that you get a read timeouts). For RAID sets,
it causes erratic performance.

-- 
Konstantin Olchanski
Data Acquisition Systems: The Bytes Must Flow!
Email: olchansk-at-triumf-dot-ca
Snail mail: 4004 Wesbrook Mall, TRIUMF, Vancouver, B.C., V6T 2A3, Canada