Difference between full write and full write-ahead

Dear Lucas,

The reserved space for full write indicates the space threshold for triggering a system to enter the write protection mode. When the remaining space of a storage pool is less than or equal to the reserved space for full write, the storage pool is filled up.

The reserved space for full write-ahead indicates the space threshold for triggering a system to enter the write through mode. When the remaining space of a storage pool is less than or equal to the reserved space for full write-ahead, the storage pool is going to be filled up.

Full write

• Reserved space

a. 20 GB

b. 1 GB space is reserved for each thin LUN, thin FS, snapshot, and thick LUN with asynchronous remote replications in a storage pool. The total reserved space depends on the specific number of the thin LUNs, thin FSs, snapshots, and thick LUNs with asynchronous remote replications in the storage pool.

c. Watermark for the total space of a storage pool: 5%

The reserved space is subject to the minimum one among the preceding values.

• Criteria

The remaining space of a storage pool is less than or equal to its reserved space for full write.

• Policy

All LUNs and FSs in the storage pool are write-protected.

Full write-ahead

• Reserved space

The reserved space for full write-ahead is an integral multiple of the reserved space for full write. Currently, the reserved space for full write-ahead is four times larger than the reserved space for full write.

• Criteria

The remaining space of a storage pool is less than or equal to its reserved space for full write-ahead.

• Policy

Thin LUNs, thin FSs, and thick LUNs with asynchronous remote replications in a storage pool are enabled with write through.

Thanks.