Enabling barriers since 2.6.9 and hdparm question

Posted May 22, 2008 11:33 UTC (Thu) by zmi (guest, #4829)
In reply to: Enabling barriers since 2.6.9 and hdparm question by pr1268
Parent article: Barriers and journaling filesystems

> What is the effect of toggling the disk drive's write-caching feature

Turning off write caches of disks and the RAID controller slows writing 
badly. Examples of a recent HP ML350 server with 3x 146GB 10k SAS disks:
- disk cache and RAID write cache OFF: 65MB/s
- disk cache and RAID write cache ON: 145MB/s
and that is on _sequential_ writes. We didn't measure _random_ writes, but 
the system felt like an old 386 then. Really unusable.

Enabling barriers since 2.6.9 and hdparm question

Posted May 22, 2008 13:40 UTC (Thu) by NAR (subscriber, #1313) [Link]

Interestingly we've had different experience - turning off the write cache actually improved
performance. I'm not sure why, but the whole system was somewhat complicated and we had data
loss. Turning off the write cache solved the data loss problem and had this surprising
side-effect too.