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Re: Should SQLite users be setting barrier=1?



On 07/13/2010 09:47 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?

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.

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?

Thanks,
Dan.



Hi Dan,

If you do not use barriers, your storage device could very well lose data if it loses power. There is no easy answer, you need to understand the type and configuration of your storage.

For a local SAS/S-ATA drive, you should have barriers enabled when the write cache is enabled (check that with hdparm for example on S-ATA). Note that you could also be safe by disabling the write cache and leaving barriers off as well.

If you have a non-volatile write cache (for example on an external, enterprise class array), you can safely mount without barriers.

Regards,

Ric


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