`iscsi` Provider

The iscsi provider provides probes for tracing iSCSI target activity.

This is a USDT provider built into the iSCSI target daemon (iscsitgtd). As a USDT provider the name is concatenated with the process ID of the daemon (eg. iscis123).

Since this provider instruments the iSCSI target daemon, DTrace commands and scripts must be run on the iSCSI target server to observe these probes.

Probes

SCSI Event	Probes
SCSI command/response	`iscsi:::scsi-command` `iscsi:::scsi-response`
Data out/in/request (rtt)	`iscsi:::data-send` `iscsi:::data-receive` `iscsi*:::data-request`
Login and logout command/response	`iscsi:::login-command` `iscsi:::login-response` `iscsi:::logout-command` `iscsi:::logout-response`
NOP out/in (pings)	`iscsi:::nop-receive` `iscsi:::nop-send`
Text and task command/response	`iscsi:::task-command` `iscsi:::task-response` `iscsi:::text-command` `iscsi:::text-response`
Asynchronous message from target	`iscsi*:::async-send`

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Arguments

Probes	Variable	Type	Description
*	`args[0]`	`conninfo_t *`	connection info
*	`args[1]`	`iscsiinfo_t *`	common iSCSI properties
`scsi-command`	`args[2]`	`iscsicmd_t *`	SCSI opcode

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Types

conninfo_t

typedef struct conninfo {                                                       
        string ci_local;         /* local host IP address */               
        string ci_remote;        /* remote host IP address */     
        string ci_protocol;      /* protocol ("ipv4", "ipv6") */               
} conninfo_t;

iscsiinfo_t

typedef struct iscsiinfo {
	string ii_target;		/* target iqn */
	string ii_initiator;		/* initiator iqn */
	uint64_t ii_lun;		/* target logical unit number */

	uint32_t ii_itt;		/* initiator task tag */
	uint32_t ii_ttt;		/* target transfer tag */

	uint32_t ii_cmdsn;		/* command sequence number */
	uint32_t ii_statsn;		/* status sequence number */
	uint32_t ii_datasn;		/* data sequence number */

	uint32_t ii_datalen;		/* length of data payload */
	uint32_t ii_flags;		/* probe-specific flags */
} iscsiinfo_t;

iscsicmd_t

typedef struct iscsicmd {
        uint64_t ic_len;        /* CDB length */
        uint8_t *ic_cdb;        /* CDB data */
} iscsicmd_t;

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Examples

One-liners

Frequency of iSCSI command types:

# dtrace -n 'iscsi*::: { @[probename] = count(); }'

Frequency of iSCSI client IP addresses:

# dtrace -n 'iscsi*::: { @[args[0]->ci_remote] = count(); }'

Payload bytes by iSCSI command type:

# dtrace -n 'iscsi*::: { @[probename] = sum(args[1]->ii_datalen); }'

Payload byte distribution by iSCSI command type:

# dtrace -n 'iscsi*::: { @[probename] = quantize(args[1]->ii_datalen); }'

iscsiwho.d

This is a simple script to produce a report of the remote IP addresses and a count of iSCSI events. This is intended to provide a quick summary of iSCSI activity when run on the iSCSI target server:

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
        printf("Tracing... Hit Ctrl-C to end.\n");
}

iscsi*:::
{
        @events[args[0]->ci_remote, probename] = count();
}

dtrace:::END
{
        printf("   %-26s %14s %8s\n", "REMOTE IP", "iSCSI EVENT", "COUNT");
        printa("   %-26s %14s %@8d\n", @events);
}

This output shows the host and the number of iSCSI operations:

# ./iscsiwho.d 
Tracing... Hit Ctrl-C to end.
^C
   REMOTE IP                     iSCSI EVENT    COUNT
   192.168.1.109                 nop-receive        1
   192.168.1.109                    nop-send        1
   192.168.1.109               scsi-response      126
   192.168.1.109                scsi-command      208
   192.168.1.109                data-receive     1207
   192.168.1.109                data-request     1207
   192.168.1.109                   data-send     1290

The fields are:

field	description
`REMOTE IP`	IP address of the client
`iSCSI EVENT`	iSCSI event type
`COUNT`	Number of events traced

The example output shows normal traffic. For this simple script, these event names are not translated beyond their iSCSI provider probe names, and require some thought to comprehend (they are from the perspective of the iSCSI target server).

An interpretation for some of these events are:

iSCSI event	Interpretation
`scsi-command`	A SCSI command was issued, such as a read or a write. Use other scripts for a breakdown on the SCSI command type.
`data-send`	Data was sent from the iSCSI target server to the client; the client is performing a read.
`data-receive`	Data was received on the iSCSI target server from the client. The client is performing a write.

iscsi Provider