Hi, I am very excited about the new journaling feature for RAID in md and want to try it out soon. Neil's article on LWN already gave a great overview and some hints about it, but I am still a little unsure about the technical requirements for the journal device. E.g. speed, reliability and size-wise. And what the implications of failing them means. I want to setup a small home NAS. My personal priorities are: Firstly, low power-per-GB as it will be solar powered and battery backed. Second priority is reliability. Performance is not that important to me. My current plan: Tiny ARM-based computer (Odroid C1+: 4x USB (2.0, unfortunately) ports), 4x 2TB SATA HDDs (@0.7W idle, 1.7W max. each) + SATA-to-USB -> RAID5, microSD for OS + applications, an eMMC for a RAID journal. (later, once they hopefully get available in April, switch to the Turris Omnia which is ARM-based again but has mini-PCIe, too, where I would attach mini-PCIe-to-SATA adapters) Is it a stupid idea to use an eMMC for the journal in the first place? I am unsure how quickly it would wear out. And seems like I do not have SMART for it either... So it would probably fail badly at some point. Is that an issue, can I simply replace the eMMC then without any data loss? Will the current code at least try a write-through directly to the HDDs once a journal disk throws errors? Does MD assume that an underlying device performs some sort of wear leveling if necessary like SSDs do for instance - or does MD itself distribute writes evenly over the journaling disk? (Does anyone know whether eMMCs usually do some kind of wear leveling?) Thanks for all your work on this awesome new feature! (and special thanks to Neil for all the years of maintenance - it is a pitty you have to step down :( ) Regards, Linus -- 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
