IBM eServer Cluster 1600 Managed by PSSP 3.5: What's New

Chapter 4. Parallel System Support Program 3.5 enhancements 85

Example 4-9 vsdatalst output

root $ vsdatalst -n

VSD Node Information

Initial Maximum VSD rw Buddy Buffer

node VSD IP packet cache cache request request minimum maximum size: #

number host_name adapter size buffers buffers count count size size maxbufs

------ --------------- -------- --------- ------- ------- ------- ------- ------- ------- -------

1 sp6n01e0 css0 61440 64 256 256 48 4096 131072 4

3 sp6n03e0 css0 61440 64 256 256 48 4096 131072 4

10 sp6n10e0 css0 61440 64 256 256 48 4096 131072 4

12 sp6n12e0 css0 61440 64 256 256 48 4096 131072 4

There is no user command to display the current size of your buddy buffers, only

what the minimum and maximum sizes are set to.

4.6.6 IP flow control

IP flow control has been added to nodes that are running VSD V3.5 or later. The

device driver will only implement the flow control if both the source and target

support it. This is not user configurable and cannot be switched off.

The client node sends a read request to the server node to access data on one of

the Virtual Shared Disks it possesses. The server then does the I/O on the

requested data and sends it back to the client. After the data is received by the

client, it sends an acknowledgement (ACK) back to the server to acknowledge

that the data has been received successfully. The ACK contains the identifiers of

all packets successfully received. The server will resend any packets that have

not been ACKed after a timeout period is reached. For a typical 256 KB request

made up of five packets, there would be one ACK after the five packets have

been received. This is shown in Figure 4-5 on page 86.

86 IBM ^ Cluster 1600 Managed by PSSP 3.5: What’s New

Figure 4-5 IP flow control: Read

A write request is received by the server. It then allocates a buddy buffer to hold

the arriving data and responds saying that it is ready for the client to send. On

receipt of this, the client sends the data to the server. The server responds with

an ACK to the client stating which packets have been received. The client has

timers running so that if not all packets are ACKed, and the timeout period is

reached, the lost packets are resent from the server again. After all the data is

received, the server starts committing the data to the VSD volume. When the

data is committed, a reply is sent to the client informing it of the completed I/O.

This is shown in Figure 4-6 on page 87.

Read Request

Do I/O

Send Response/Data

ACK