Re: [patch] ext2/3: document conditions when reliable operation ispossible

From: david
Date: Tue Aug 25 2009 - 19:49:49 EST

On Tue, 25 Aug 2009, Ric Wheeler wrote:

On 08/25/2009 07:26 PM, Pavel Machek wrote:

Basically, any file system (Linux, windows, OSX, etc) that writes into
the page cache will lose data when you hot unplug its storage. End of
story, don't do it!

No, not ext3 on SATA disk with barriers on and proper use of
fsync(). I actually tested that.

Yes, I should be able to hotunplug SATA drives and expect the data
that was fsync-ed to be there.

You can and will lose data (even after fsync) with any type of storage at
some rate. What you are missing here is that data loss needs to be
measured in hard numbers - say percentage of installed boxes that have
config X that lose data.

I'm talking "by design" here.

I will lose data even on SATA drive that is properly powered on if I
wait 5 years.


You are dead wrong.

For RAID5 arrays, you assume that you have a hard failure and a power outage before you can rebuild the RAID (order of hours at full tilt).

and that the power outage causes a corrupted write.

I can promise you that hot unplugging and replugging a S-ATA drive will
also lose you data if you are actively writing to it (ext2, 3, whatever).

I can promise you that running S-ATA drive will also lose you data,
even if you are not actively writing to it. Just wait 10 years; so
what is your point?

I lost a s-ata drive 24 hours after installing it in a new box. If I had MD5 RAID5, I would not have lost any.

me to, in fact just after I copied data from a raid array to it so that I could rebuild the raid array differently :-(

David Lang
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