Rebuilding failed drives with reduced write overhead

A computer program product (CPP) for rebuilding a drive in a redundant array of independent disks (RAID) array, the computer program product comprising:

• a set of one or more computer-readable storage media;
• and
• program instructions, collectively stored in the set of one or more storage media, for causing a processor set to perform the following computer operations:
• in response to a failed drive in the RAID array being replaced with a replacement drive,
• and in response to determining the replacement drive cannot be pre-formatted, initialize a high water mark;
• recreate blocks of data that were stored in the failed drive using an exposed mode read with zero detect operation;
• and
• in response to determining one or more of the recreated blocks are equivalent to deallocated blocks, cause corresponding blocks in the replacement drive to be deallocated.

A computer system (CS) for rebuilding a drive in a redundant array of independent disks (RAID) array, the computer system comprising:

• a processor set;
• a set of one or more computer-readable storage media;
• and
• program instructions, collectively stored in the set of one or more storage media, for causing the processor set to perform the following computer operations:
• in response to a failed drive in the RAID array being replaced with a replacement drive;
• and in response to determining the replacement drive cannot be pre-formatted, initialize a high water mark;
• recreate blocks of data stored that were in the failed drive;
• and
• in response to determining one or more of the recreated blocks are equivalent to deallocated blocks, cause corresponding blocks in the replacement drive to be deallocated,
• wherein the drives in the RAID array are selected from the group consisting of:
• solid state drives (SSDs), hard disk drives (HDDs), and magnetic tape drives.

A computer-implemented method (CIM) for rebuilding a drive in a redundant array of independent disks (RAID) array, the method comprising:

• in response to a failed drive in the RAID array being replaced with a replacement drive and a determination that the replacement drive cannot be pre-formatted, initializing a high water mark;
• recreating blocks of data that were stored in the failed drive;
• in response to determining one or more of the recreated blocks are not equivalent to deallocated blocks, causing data in the one or more recreated blocks to be written to corresponding blocks in the replacement drive;
• in response to determining one or more of the recreated blocks are equivalent to deallocated blocks, causing corresponding blocks in the replacement drive to be deallocated;
• and
• advancing the high water mark to incorporate the corresponding blocks in the replacement drive.

A computer program product (CPP) for rebuilding a drive in a redundant array of independent disks (RAID) array, the computer program product comprising:

• a set of one or more computer-readable storage media;
• and
• program instructions, collectively stored in the set of one or more storage media, for causing a processor set to perform the following computer operations:
• in response to a failed drive in the RAID array being replaced with a replacement drive and determining that the replacement drive cannot be pre-formatted, initializing a high water mark;
• recreating blocks of data that were stored in the failed drive;
• in response to determining one or more of the recreated blocks are not equivalent to deallocated blocks, causing data in the one or more recreated blocks to be written to corresponding blocks in the replacement drive;
• in response to determining one or more of the recreated blocks are equivalent to deallocated blocks, causing corresponding blocks in the replacement drive to be deallocated;
• and
• advancing the high water mark to incorporate the corresponding blocks in the replacement drive.