Re: Should SQLite users be setting barrier=1?

[Ric Wheeler <rwheeler@xxxxxxxxxx>]

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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