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Improving ext4: bigalloc, inline data, and metadata checksums

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 5, 2011 1:34 UTC (Mon) by cmccabe (guest, #60281)
In reply to: Improving ext4: bigalloc, inline data, and metadata checksums by alankila
Parent article: Improving ext4: bigalloc, inline data, and metadata checksums

walex said:
> > No journaled filesystem is good for SSDs

alankila said:
> Just to get the argument out in the open, what is the basis
> for making this claim?

Well, SSDs have a limited number of write cycles. With metadata journaling, you're effectively writing all the metadata changes twice instead of once. That will wear out the flash faster. I think a filesystem based on soft updates might do well on SSDs.

Of course the optimal thing would be if the hardware would just expose an actual MTD interface and let us use NilFS or UBIFS. But so far, that shows no signs of happening. The main reason seems to be that Windows is not able to use raw MTD devices, and most SSDs are sold into the traditional Windows desktop market.

Valerie Aurora also wrote an excellent article about the similarities between SSD block remapping layers and log structured filesystems here: http://lwn.net/Articles/353411/


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