malahal@xxxxxxxxxx wrote: > Takahiro Yasui [tyasui@xxxxxxxxxx] wrote: > ... >> When one of log disk is broken and is not recognized, there is a case >> disk that replication is executed. Let me explain with the following >> simple case, which is the mirror volume, vg00-lv00 is composed of two >> data disks and one mirrored log which is composed of two log disks. >> >> * Analysis of this problem >> >> A mirrored log is a type of "core" log and log devices need to be >> synchronized when a mirrored log is activated. But when the first log >> device is not recognized, "READ" I/O returns -EIO in disk_resume() >> because log disk is not in-sync status and a default log can not be >> switched to the other log disk working well. >> >> >> Avoiding disk replication even if a log device got trouble is one of >> the requirements. Is there any solution to avoid this problem by the >> mirrored log approach? > > Two ways to fix: > 1) Never make "error leg" as your master leg as that is pointless. This approach will solve the case that a log leg is not recognized, but I'm afraid that it won't solve other type of I/O errors, such as medium error. LVM commands such as vgchange accesses only sectors containing label and metadata, and LVM commands will successfully activate mirrored log as a userland process. However, in kernel, I/Os errors might be detected in a log area, and "READ" I/O returns -EIO. In this case, log will be detected as a failed device. > 2) Maybe we can use 'nosync' option when one of the two legs is known to > be an error device. This is probably easier than method (1) This approach looks good. Thanks, --- Takahiro Yasui Hitachi Computer Products (America), Inc. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
