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One of the key modules of the CSV file system stack is the CSV Volume Manager. This is the driver that makes sure that the CSVs are showed as local volumes. This driver sits in the volume layer and processes I/O in the Direct mode and/or in the Block Level Redirected I/O Mode.

In Direct Mode, I/O operations from the application on the cluster node can be sent directly to the storage via the Cluster Volume Manager. It therefore, bypasses the NTFS or ReFS volume stack.

In Block Level Redirected I/O Mode, I/O passes through the CSV Volume Manager in the local CSVFS proxy file system stack and is written directly to Disk.sys on the coordinator node.

By closely monitoring the I/O traffic to a CSV Volume Manager, administrators will be able to gauge the level of I/O activity on the corresponding CSV. In the process, overloaded CSVs can be isolated and the nature of I/O traffic contributing to the load - i.e., whether Direct I/O or Block Level Redirected I/O - can be pinpointed. This is exactly what the FCCluCSVVolMgrTest test. For each CSV, this test reports the rate of direct and redirected reads and writes to that CSV. This way, the test sheds light on the I/O load on every CSV, pinpoints overloaded CSVs, and thus reveals irregularities in load balancing across CSVs.

Outputs of the test : One set of results will be reported for every CSV on the server.

Measurement	Description	Measurement Unit	Interpretation
Direct_read_throughput	Indicates the rate at which this CSV reads data from the disk in the Direct I/O Mode.	Kbps
Direct_write_throughput	Indicates the rate at which this CSV writes data to the disk in the Direct I/O Mode.	Kbps
Total_direct_throughput	Indicates the rate at which this CSV reads data from and writes data to the disk in the Direct I/O Mode.	Kbps	The value of this measure is the sum of the values of the Direct_read_throughput and Direct_write_throughput measure. This is a good indicator of the level of direct I/O activity on a CSV. By comparing the value of this measure across CSVs, you can figure out which CSV is experiencing maximum direct traffic. If this max value is abnormally high for that CSV, you may want to investigate the reasons for the same.
Redirected_read_throput	Indicates the rate at which this CSV reads data from the disk by redirecting the I/O to the co-ordinator node via SMB in the Block Level Redirected I/O mode.	Kbps	The technologies that let CSV-enabled volumes operate require one cluster node that's responsible for the coordination of file access. This cluster node is called the coordinator node, with each individual LUN having its own coordinator node. I/O redirection can also occur if slave nodes in a cluster are unable to access the disk directly. In this case, the CSV Volume Manager on the slave nodes will redirect the I/O to the co-ordinator node via the SMB Client protocol. The coordinator node then processes the redirected I/O it receives using the SMB Server protocol. The Cluster Shared Volume Manager performs this redirection in the Block Level Redirected Redirected Mode only. From this, we can conclude that for a CSV attached to a slave/non-coordinator node, the value of the Redirected_read_throput measure will indicate the rate at which that CSV redirected the read I/Os to the coordinator node and read data from the disk, in the Block Level Redirected I/O Mode. For a slave/non-coordinator node, the value of the Redir_write_throughput measure will represent only the rate at which that CSV redirects write I/Os to the coordinator node and writes data to the disk, in the Block Level Redirected I/O Mode. For a Coordinator Node on the other hand, these measures denote the rate at which the Coordinator Node services read/write I/Os (as the case may be) redirected to it by all slave nodes, in the Block Level Redirected I/O Mode.
Redir_write_throughput	If the node being monitored is a co-ordinator node, then this measure indicates the rate at which this CSV writes data to the physical disk, in the Block Level Redirected I/O Mode. If the node being monitored is a non-coordinator node, then this measure indicates the rate at which this CSV writes data to the disk by redirecting the I/O to the co-ordinator node via SMB, in the Block Level Redirected I/O Mode.	Kbps
Total_redirected_throput	Indicates the rate at which this CSV writes data to the disk by redirecting the I/O to the co-ordinator node via SMB, in the Block Level Redirected I/O Mode.	Kbps	This is the sum of the values of the Redirected_read_throput and Redir_write_throughput measures. This is a good indicator of the level of redirected I/O activity on a CSV. By comparing the value of this measure across CSVs, you can figure out which CSV is experiencing maximum redirected traffic. If this max value is abnormally high for that CSV, you may want to investigate the reasons for the same.
Read_throughput	Indicates the rate at which data was read by this CSV, both directly and via redirection - i.e.,in the Direct I/O and Block Level Redirected I/O modes.	Kbps	This is the sum of the values of the Direct_read_throughput and Redirected_read_throput measures.
Write_throughput	Indicates the rate at which data was written by this CSV, both directly and via redirection - i.e.,in the Direct I/O and Block Level Redirected I/O modes.	Kbps	This is the sum of the values of the Direct_write_throughput and Redir_write_throughput measures.
Throughput	Indicates the rate at which data was read and written by this CSV, both directly and via redirection - i.e.,in the Direct I/O and Block Level Redirected I/O modes.	Kbps	This is the sum of the values of the Read_throughput and Write_throughput measures. This is a good indicator of the level of I/O activity on a CSV. By comparing the value of this measure across CSVs, you can figure out which CSV is experiencing maximum traffic. If this max value is abnormally high for that CSV, you may want to investigate the reasons for the same.
Direct_read_rate	Indicates the rate at which this CSV performs disk reads in the Direct I/O Mode.	Reads/Sec
Direct_write_rate	Indicates the rate at which this CSV performs disk writes in the Direct I/O Mode.	Writes/Sec
Total_direct_iops	Indicates the rate at which this CSV performs IOPS in the Direct I/O Mode.	Operations/Sec	This is a good indicator of the level of I/O activity on the CSV in the Direct I/O Mode.
Redirected_read_rate	If the node being monitored is a co-ordinator node, then this measure indicates the rate at which this CSV reads from the disk, in the Block Level Redirected I/O Mode. If the node being monitored is a non-coordinator node, then this measure indicates the rate at which this CSV reads from the disk by redirecting the read requests to the co-ordinator node via SMB, in the Block Level Redirected I/O Mode.	Reads/Sec
Redirected_write_rate	If the node being monitored is a co-ordinator node, then this measure indicates the rate at which this CSV writes to the disk, in the Block Level Redirected I/O Mode. If the node being monitored is a non-coordinator node, then this measure indicates the rate at which this CSV writes to the disk by redirecting the write requests to the co-ordinator node via SMB, in the Block Level Redirected I/O Mode.	Writes/Sec
Total_redirected_iops	Indicates the rate at which I/O reads and writes were performed by this CSV on the disk, in the Block Level Redirected I/O Mode.	Operations/Sec	This is a good indicator of the level of I/O activity in the Block Level Redirected I/O Mode.
Read_iops	Indicates the rate at which read I/O operations were performed on this CSV, both directly and via redirection - i.e., in the Direct I/O and Block Level Redirected I/O, Modes.	Reads/Sec	The value of this measure is the sum of the values of the Direct_read_rate and Redirected_read_rate measures.
Write_iops	Indicates the rate at which write I/O operations were performed on this CSV, both directly and via redirection - i.e., in the Direct I/O and Block Level Redirected I/O I/O Modes.	Writes/Sec	The value of this measure is the sum of the values of the Direct_write_rate and Redirected_write_rate measures.
Iops	Indicates the rate at which read and write I/O operations were performed on this CSV, both directly and via redirection - i.e., in the Direct I/O and Block Level Redirected I/O.	Operations/Sec	The value of this measure is the sum of the values of the Read_IOPS and Write_IOPS measures. This is a good indicator of the level of I/O activity on the CSV.