Hi, This patchset adds the --discard option for creating new arrays in mdadm. When specified, mdadm will send block discard (aka. trim or deallocate) requests to all of the specified block devices. It will then read back parts of the device to double check that the disks are now all zeros. If they are all zero, the array is in a known state and does not need to generate the parity seeing everything is zero and correct. If the devices do not support discard, or do not result in zero data on each disk, an error will be returned and the array will not be created. If all disks get successfully discarded and appear zeroed, then the new array will not need to be synchronized. The create operation will then proceed as if --assume-clean was specified. This provides a safe way and fast way to create an array that does not need to be synchronized with devices that support discard requests. Another option for this work is to use a write zero request. This can be done in linux currently with fallocate and the FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE flags. This will send optimized write-zero requests to the devices, without falling back to regular writes to zero the disk. The benefit of this is that the disk will explicitly read back as zeros, so a zero check is not necessary. The down side is that not all devices implement this in as optimal a way as the discard request does and on some of these devices zeroing can take multiple seconds per GB. Because write-zero requests may be slow and most (but not all) discard requests read back as zeros, this work uses only discard requests. Logan -- Logan Gunthorpe (2): mdadm: Add --discard option for Create manpage: Add --discard option to manpage Create.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ ReadMe.c | 1 + mdadm.8.in | 15 +++++++++++ mdadm.c | 4 +++ mdadm.h | 2 ++ 5 files changed, 97 insertions(+) base-commit: 171e9743881edf2dfb163ddff483566fbf913ccd -- 2.30.2
