[Lustre-discuss] Enabling Write-back cache feature

[Andreas Dilger]

On Dec 04, 2008  14:57 +0530, siva murugan wrote:
> how to enable write-back cache in mdt .? is this feature available in lustre
> 1.6.5.1 ? or planned in the future roadmap

The MDT always does writeback caching, and the clients will recover this
state if the MDS crashes.

What isn't supported is to have the disk itself do writeback caching[*]
because the ext3 journaling code does not get notified correctly when
data is on disk.

[*] write cache can be enabled on disks if "barriers" are enabled, but
    this often provides worse performance on RAID hardware because in
    Linux barriers are implemented by flushing the entire disk cache
    instead of just disallowing reordering of IO requests.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.