What do I need to know about host block size requirements?

Contributors netapp-jolieg netapp-jsnyder

For EF300 and EF600 systems, a volume can be set to support a 512-byte or a 4KiB block size (also called "sector size"). You must set the correct value during volume creation. If possible, the system suggests the appropriate default value.

Before setting the volume block size, read the following limitations and guidelines.

  • Some operating systems and virtual machines (notably VMware, at this time) require a 512-byte block size and do not support 4KiB, so make sure you know the host requirements before creating a volume. Typically, you can achieve the best performance by setting a volume to present a 4KiB block size; however, ensure that your host allows for 4KiB (or “4Kn”) blocks.

  • The type of drives you select for your pool or volume group also determines what volume block sizes are supported, as follows:

    • If you create a volume group using drives that write to 512-byte blocks, then you can only create volumes with 512-byte blocks.

    • If you create a volume group using drives that write to 4KiB blocks, then you can create volumes with either 512-byte or 4KiB blocks.

  • If the array has an iSCSI host interface card, all volumes are limited to 512-byte blocks (regardless of volume group block size). This is due to a specific hardware implementation.

  • You cannot change a block size once it is set. If you need to change a block size, you must delete the volume and re-create it.