NVMe-oF Limitations and Operating Guidance

Present each namespace to exactly one DSX node. Use the array’s host access configuration, with each DSX node’s host NQN, so that no other host can see the namespace. Hammerspace lets a second DSX node connect a subsystem that another node already uses, and refuses only the creation of a logical volume on it (One or more of the specified NVMe-oF subsystems is already connected to another node); it cannot stop a host outside Hammerspace from writing to a namespace. Two hosts writing to one namespace corrupt its file system.

Give the enclosure every address that the array presents its subsystems on when you add it. Hammerspace connects a subsystem to the addresses that are known when the subsystem is connected. An address added to the enclosure later is listed, but the connected subsystems are not connected to it, even though the listing shows the new address as CONNECTED. To add a path to a subsystem that is already connected, disconnect and reconnect the subsystem, which you can do only while none of its namespaces has a logical volume.

Do not present a clone or snapshot of a namespace to the same DSX node as the original. Namespaces that carry the same file system UUID are not supported, and Hammerspace may be unable to mount a volume on either of them.

If a connection to a subsystem fails with a general error, check that the array presents that subsystem to the DSX node’s host NQN. The error does not say that access was refused.

Each DSX node generates its host NQN once, when it is first configured, and you cannot change it. Never copy one DSX node’s host NQN to another host or edit it. Two hosts that present the same NQN are not detected and are not supported.

Reinstalling a DSX node gives it a new host NQN. Update the array’s host access configuration with the new NQN before you reconnect the node’s enclosures.

Hammerspace connects and disconnects whole subsystems. You cannot disconnect a single namespace.

You cannot disconnect a subsystem while any of its namespaces has a logical volume. Remove the Hammerspace volume and delete the logical volume first. Otherwise the command fails with the message Unable to disconnect NVMe-oF subsystem(s), one or more subsystems have active volumes.

Right after a subsystem is connected, a namespace can take a short time to appear. If a namespace you expect is missing, repeat the operation.

Changing any connection setting other than the I/O policy reconnects the enclosure’s controllers. See Controller Loss Timeout.