On 09/19/2012 07:28 PM, ching wrote:

can anybody helps?

On 09/17/2012 07:15 PM, ching wrote:

quoted

I am testing btrfs for long-term storage and backup, and i would like
to know more about "autodefrag" option:

1. Will "autodefrag" option benefit ssd?

    My understanding is:

       autodrag -> number of extent decrease -> metadata decrease -> a
"healthier" filesystem in the long run

   (P.S. I am aware that autodefrag will introduce extra write I/O)

Yes, your understanding is right, random write workloads will benefit from it.

quoted

2. AFAIK, "autodefrag" detects small random writes into files and
queues them up for an automatic defrag process, so the filesystem will
defragment itself while it's used.

    If the system reboot/crash/remount-ro, will the autodefrag process
continue after resume?

For reboot, autodefrag will be waited to finish during umounting btrfs.

For crash and remount-ro, it won't resume since it is not that necessary and we're all
COWed so that the data is ok.

And autodefrag will only take effect when taking the 'autodefrag' mount option.

thanks,
liubo

quoted

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