On Sunday, January 8th, 2023 at 22:20, anthony <antmbox@xxxxxxxxxxxxxxx> wrote: > I'm GUESSING you're trying to move from a non-raid setup. First of all, thank you for taking the time to respond. But no, I really am just asking about how and when the parity chunks get distributed across a new device when a md-raid6 group is grown. There was a time when some raid systems (not naming names, and if I remember correctly) would NOT re-distribute parity chunks on a grown group. If the group was built with devices A, B, C, & D, then the parity chunks would remain on those four devices, and added devices E & F, etc. would only ever have data chunks, since the placement of parity chunks in a stripe was only done at initial group creation time, even if the stripe was extended to additional devices. I'm not questioning that growing a md-raid group works and is fully functional. This is very much a "what happens behind the curtain" question. I don't know how md-raid6 works at this low and internal level, hence the question. Does the re-sync triggered by the grow re-write the entirety of all stripes and some P & Q chunks get moved to the new device? If the re-sync does change some P & Q chunks to data chunks to place those parity chunks on the new device, is the layout identical to what it would be if the group was created with all devices instead of being grown? Does it happen when a stripe is re-written through normal activity? this implies if a stripe never gets any write activity, it will never re-layout the location of its P & Q chunks. Does it happen at all? And the new devices only ever have data chunks like what I remember from older systems? Thank you!
