On Mon, Feb 20, 2017 at 05:50:09PM +0100, Christian Samsel wrote: > Hello raid team, > First of all, thanks for your work. > So i recently read about Linux raid5/raid6 write-cache and journaling and thought about > giving it a try. I'm mainly interested in the additional safety provided by the journal but might > want be future proof to use the write cache as well. > I read how to create an array using a journal but i havent found the slightest indication of how > large the respective device/partition should be. I went through the lwn article [1], the slides [2] of the > respective engineers at facebook and a few commit messages. > > So my question is, let's assume i have a 6TB raid5 array (3x3TB), what would a good journal device size be? > I'd probably went with 4GB, as this is kinda the upper bound of what hardware raid controller offer. Thanks for trying! Depending on write-through or write-back mode. For write-through mode, the size could be just several hundreds megabytes. For write-back mode, the size should be a little bigger, several gigabytes, but 4 GB should be enough. Also I added doc about raid5-cache in kernel_source/Documentation/md/raid5-cache.txt recently. Thanks, Shaohua -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
