[Gluster-users] Small File and "ls" performance ..

[Barry Jaspan]

I am concerned about this patch:

updated write-behind default values - http://patches.gluster.com/patch/3223/
>

It changes the default value for performance/writebehind's flush-behind
option from off to on. My understanding is that when flush-behind is off,
all writes are done in the background but flush/close are blocking, which
means they can return a valid error code. When flush-behind is on, the
flush/close are also done in the background and so must always return
success---which means an application has no way to know if the write really
succeeded.

There are certainly use cases where "fire and forget" is a valid write
strategy. However, silently changing the DEFAULT behavior for something this
critical to reliability does not seem like a good idea.

Regarding Joshua's performance test results with untar'ing the linux kernel,
I'm not at all surprised that he got such a huge speedup. However, the
results are not really comparable, because one set was obtained with
reliable writes, and the other was not.

Barry