3d31aad83e
Instead of choosing a leaf vdev quasi-randomly, by starting at the root vdev and randomly choosing children, rotate over leaves to issue MMP writes. This fixes an issue in a pool whose top-level vdevs have different numbers of leaves. The issue is that the frequency at which individual leaves are chosen for MMP writes is based not on the total number of leaves but based on how many siblings the leaves have. For example, in a pool like this: root-vdev +------+---------------+ vdev1 vdev2 | | | +------+-----+-----+----+ disk1 disk2 disk3 disk4 disk5 disk6 vdev1 and vdev2 will each be chosen 50% of the time. Every time vdev1 is chosen, disk1 will be chosen. However, every time vdev2 is chosen, disk2 is chosen 20% of the time. As a result, disk1 will be sent 5x as many MMP writes as disk2. This may create wear issues in the case of SSDs. It also reduces the effectiveness of MMP as it depends on the writes being evenly distributed for the case where some devices fail or are partitioned. The new code maintains a list of leaf vdevs in the pool. MMP records the last leaf used for an MMP write in mmp->mmp_last_leaf. To choose the next leaf, MMP starts at mmp->mmp_last_leaf and traverses the list, continuing from the head if the tail is reached. It stops when a suitable leaf is found or all leaves have been examined. Added a test to verify MMP write distribution is even. Reviewed-by: Tom Caputi <tcaputi@datto.com> Reviewed-by: Kash Pande <kash@tripleback.net> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: loli10K <ezomori.nozomu@gmail.com> Signed-off-by: Olaf Faaland <faaland1@llnl.gov> Closes #7953 |
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linux.run | ||
longevity.run | ||
Makefile.am | ||
perf-regression.run |