[mythtv-users] Where the bottleneck?

Mitch Gore mitchell.gore at gmail.com
Sat Jan 26 16:14:03 UTC 2008


Run hdparm -Tt on the SATA drives. If you get I/O greater than, say, 8

> megabytes a second, then I'm pretty sure DMA is enabled (my experience
> with older IDE drives was that they maxed out at about 4 megs per
> second (at the most) if DMA was disabled, regardless of drive or CPU
> speed). For example - on one system here "hdparm /dev/sdb" shows no
> way to control DMA, but when using "-Tt" shows a raw read rate of
> about 74 megs/second (cached from controller is 220/megs/second), so
> I'm pretty certain DMA IS enabled.
>
> Calvin
>

[root at mythtv ~]# hdparm -Tt /dev/sda

/dev/sda:
 Timing cached reads:   1330 MB in  2.00 seconds = 665.24 MB/sec
 Timing buffered disk reads:   76 MB in  3.05 seconds =  24.96 MB/sec
[root at mythtv ~]# hdparm -Tt /dev/sdb

/dev/sdb:
 Timing cached reads:   1516 MB in  2.00 seconds = 757.98 MB/sec
 Timing buffered disk reads:  126 MB in  3.03 seconds =  41.65 MB/sec
[root at mythtv ~]# hdparm -Tt /dev/sdc

/dev/sdc:
 Timing cached reads:   1416 MB in  2.00 seconds = 707.76 MB/sec
 Timing buffered disk reads:   96 MB in  3.48 seconds =  27.59 MB/sec
[root at mythtv ~]#
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