Monday, 26 January 2015

Re: Creating Ubuntu USB sticks

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On 26.01.2015 17:49, Phillip Susi wrote:
> On 1/22/2015 10:22 AM, Stefan Bader wrote:
>> That is the expected behaviour with that incantation. If you added
>> a "oflag=sync" dd should return only after write has finished. In
>> your case you use cached writes.
>
> oflag=sync is terrible and should never be used as it does the
> equivalent of fsync() after every single write(). Not only does this
> cause terrible performance, but in the case of flash, will wear it out
> much more. Use conv=fsync instead to fsync() once, at the end.

You are right, as long as one does not also use bs=1M (for example). Which I
should have added. I usually add that without thinking, so I forgot. Which
causes bigger write sizes, so the performance is good. That blocksize should
also cover multiple erase blocks, so the wearout is no worse than with
conv=fsync (where the blocklayer may merge the defaul 512b request if no bs is
given).