Messages in this thread | | | Date | Sun, 29 May 2005 23:16:10 +0200 | From | Matthias Andree <> | Subject | Re: Linux does not care for data integrity (was: Disk write cache) |
| |
On Sun, 29 May 2005, Greg Stark wrote:
> Oracle, Sybase, Postgres, other databases have hard requirements. They > guarantee that when they acknowledge a transaction commit the data has been > written to non-volatile media and will be recoverable even in the face of a > routine power loss. > > They meet this requirement just fine on SCSI drives (where write caching > generally ships disabled) and on any OS where fsync issues a cache flush. If
I don't know what facts "generally ships disabled" is based on, all of the more recent SCSI drives (non SCA type though) I acquired came with write cache enabled and some also with queue algorithm modifier set to 1.
> Worse, if the disk flushes the data to disk out of order it's quite > likely the entire database will be corrupted on any simple power > outage. I'm not clear whether that's the case for any common drives.
It's a matter of enforcing write order. In how far such ordering constraints are propagated by file systems, VFS layer, down to the hardware, is the grand question.
-- Matthias Andree - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |