Artur Paszkiewicz <artur.paszkiewicz@xxxxxxxxx> writes: > On 11/29/2016 04:23 PM, Jes Sorensen wrote: >> Artur Paszkiewicz <artur.paszkiewicz@xxxxxxxxx> writes: >>> On 11/29/2016 12:51 AM, Jes Sorensen wrote: >>>>> @@ -3177,6 +3195,9 @@ static void getinfo_super_imsm(struct >>>>> supertype *st, struct mdinfo *info, char * >>>>> >>>>> disk = &super->disks->disk; >>>>> info->data_offset = total_blocks(&super->disks->disk) >>>>> - reserved; >>>>> + /* mpb anchor sector - see store_imsm_mpb() */ >>>>> + info->sb_start = total_blocks(&super->disks->disk) - >>>>> + ((2 * super->sector_size) >> 9); >>>>> info->component_size = reserved; >>>>> info->disk.state = is_configured(disk) ? (1 << >>>>> MD_DISK_ACTIVE) : 0; >>>>> /* we don't change info->disk.raid_disk here because >>>> >>>> Hi Artur, >>>> >>>> I have been sitting staring at the above for a while, and looking at >>>> store_imsm_mpb() it is not clear to me what is meant to happen here. >>>> >>>> For 4k sector drives, aren't you pushing back sb_start way further than >>>> you are for 512 byte sector drives? Ie. you are subtracting 16 sectors >>>> for the 4k drive but only two sectors for the 512 byte sector drive? >>>> >>>> Maybe it's because it's Monday or I lost the last of my marbles, but >>>> could you possibly enlighten me here please? >>> >>> Jes, >>> >>> You read it correctly. The reason for this is that the IMSM anchor is >>> located in the second _logical_ sector from the end of the drive. So for >>> 4k drives this will be 16 512-byte sectors from the end. >> >> I see, so the IMSM implementation uses 512 byte logical sectors on top >> of 4k drives? Could I ask you to add a note explaining this in the code? > > IMSM uses logical (4k or 512b) sector sizes in the metadata, but mdadm > implementation uses just 512 byte sectors. This is how it works since > Pawel's 4k support patches - it converts 4k metadata internally to 512b > sector values. Plus here the sb_start value is passed to the kernel, so > it must be in 512 byte sectors. Sure, I can add a comment about this. Great, I prefer to have it documented so nobody else tries to pull all their hairs out trying to understand it :) Thanks, Jes -- 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
