Re: Should SQLite users be setting barrier=1?
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On 07/13/2010 08:47 AM, Dan Kennedy wrote: > Hi, > > Should sqlite users who are paranoid about losing data > when hard resets occur be setting the barrier=1 mount > option with ext3? barriers should be enabled whenever you wish to ensure a consistent filesystem post-powerloss, and you have write caches on your drives which may reorder or lose data when power is lost. Whether your resets drop power to drive caches, I dunno. > The situation is that we think SQLite has written data > to a series of 4K blocks in a file and then called > fsync() on the file descriptor. After this a hard reset > occurs. Upon recovery it seems like one of the 4K blocks > has been zeroed. The others are all fine. See ext3_sync_file: /* * In case we didn't commit a transaction, we have to flush * disk caches manually so that data really is on persistent * storage */ if (needs_barrier) blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL, BLKDEV_IFL_WAIT); so w/o barriers you are not flushing the drive cache and that data will be lost. > Happens every now and again under stress testing. > > System is using data=journaled, but not barrier=1. > > Should users also be setting barrier=1 for extra robustness > in the face of hard resets? s/extra// - but yes. -Eric > Thanks, > Dan. > > _______________________________________________ > Ext3-users mailing list > Ext3-users@xxxxxxxxxx > https://www.redhat.com/mailman/listinfo/ext3-users _______________________________________________ Ext3-users mailing list Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
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