Adaptive throttling for fiber channel disks

Details Adaptive throttling for fiber channel disks Adaptive throttling for fiber channel disks

2000-07-05

2003-10-21

Gaffin, Jeffrey (Department: 2182)

Electrical computers and digital data processing systems: input/

Input/output data processing

Input/output process timing

C710S029000, C710S052000, C710S053000, C710S054000, C710S056000, C710S057000, C710S310000

Reexamination Certificate

active

06636909

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to control of storage devices in general, and more specifically to a device driver for a storage device employing an adaptive throttling technique that dynamically reduces/increases the number of commands that can be issued to a storage device, such as a Fiber Channel disk, to avoid overloading the storage device.
BACKGROUND OF THE INVENTION
Increasing demand on computer network systems has created a need for high-performance communications between servers and storage devices and servers and other devices. Fiber Channel is a high-speed, full-duplex, serial data transfer architecture that uses optical fiber to connect various devices such as servers and storage devices. Fiber Channel supports multiple protocols including Small Computer System Interface (SCSI) and Internet Protocol (IP). Storage devices connected to a Fiber Channel network operate with both SCSI and networking (IP) protocols. Servers and workstations can use the Fiber Channel network for high-speed, shared access to the same storage device or system such as a Redundant Array of Independent Disks (RAID). Fiber Channel has supported both peer-to-peer and arbitrated loop topologies and will support a fabric topology.
FIG. 1
is a block diagram illustrating a Fiber Channel peer-to-peer network. This topology consists of a single computer
100
and a single storage device
110
such as an individual disk or a disk array. The computer
100
and the storage device
110
are interconnected using a Fiber Channel cable
105
. The computer
100
can communicate with the storage device
110
using Fiber Channel protocol transmitted over the Fiber Channel cable
105
. The Fiber Channel protocol can contain SCSI commands issued by the computer
100
to the storage device
110
.
FIG. 2
is a block diagram illustrating a Fiber Channel arbitrated loop network. This topology consists of at least one computer
200
and several other devices
210
,
215
, and
220
. These devices can be storage devices such as a disks or arrays of disks, printers, or other peripheral devices. These devices are interconnected using a Fiber Channel cable
205
. The computer
200
can communicate with the other devices
210
-
220
using Fiber Channel protocol transmitted over the Fiber Channel cable
205
. Control of the loop can be based on token passing or another arbitration scheme. When the computer
200
communicates with storage devices in the network, the Fiber Channel protocol can contain SCSI commands issued by the computer
200
to the storage device.
FIG. 3
is a block diagram illustrating a Fiber Channel fabric based network. This topology consists of at least one computer
300
, at least one switch
310
, and a number of other devices
315
-
325
. These devices can consist of other computers, other switches, disks, printers or other peripheral devices. These devices are interconnected using a Fiber Channel cable
305
. The nature of such a fabric allows the network to be easily expanded and creates great flexibility. Therefore, many layouts different from that illustrated in
FIG. 3
can be imagined. The computer
300
can communicate with other devices
315
-
325
on the fabric through the switch
310
. To communicate with a storage device the computer
300
transmits a frame containing Fiber Channel protocol and SCSI commands through the switch
310
to the storage device.
In each topology a problem can arise when Fiber Channel is used to connect a Fiber Channel SCSI disk drive. For these drive types, the Fiber Channel commands along with the SCSI commands require more memory, firmware code, and time for the processors in the storage devices to handle than SCSI commands alone. This increased processing time combined with the increased speed of the Fiber Channel network means that the storage device's processor may not be able to respond before the arrival of the next frame. Since the storage device has an internal queue, this is normally not a problem. However, if the queue becomes full, the computer may send additional frames before the storage device can signal the full condition to the computer.
FIG. 4
is a block diagram illustrating exemplary handshaking between an initiator and a storage device. In this example a computer
400
issues a write command
405
to a disk drive. Normally, a write command
405
generated at the computer
400
is submitted to the file system
410
. The file system
410
then passes the write command
405
to the software disk driver
415
that issues the command to a bus interface
420
, such as a host bus adapter. The bus interface
420
is connected to a disk
435
. The bus interface issues the write command to the disk
435
that then processes the command and responds back
425
to the bus interface
420
. The bus interface
420
then passes the response back to the software disk driver
415
. Finally, completion information associated with the response may be provided by the software disk driver
415
to the file system
410
.
FIG. 5
is a block diagram illustrating a computer
500
issuing a write command
505
to a disk drive
535
when the disk's queue is full. Normally, the write command
505
generated at the computer
500
is submitted to the file system
510
. The file system
510
then passes the write command to the software disk driver
515
which issues the command to a bus interface
520
such as a host bus adapter. The bus interface
520
issues the write command
530
to the disk
535
which then processes the command and responds back
525
to the bus interface
520
. The bus interface
520
then passes the response back to the software disk driver
515
. Finally, completion information associated with the response may be provided by the software disk driver
515
to the file system
510
.
When the disk
535
receives the command, the disk temporarily stores the command in a queue (not shown) until it can be processed. If the queue becomes full, the disk
535
returns a queue full signal
525
to the bus interface
520
. Additionally, if the host bus adapter is busy, it may return a busy signal to the software disk driver
515
. In either case the command has returned to the software disk driver
515
without being processed by the disk
535
.
Since the Fiber Channel protocol may include SCSI commands as well as other commands, the Fiber Channel protocol is more processor intensive than SCSI alone. Consequently, the processing of Fiber Channel protocol takes considerably longer. Typically, SCSI disks can respond to a write request with a queue full signal quickly. However, because of the increased load on the disk's processing resources due to the Fiber Channel protocol, a disk connected to a Fiber Channel network may take longer than normal to respond to a write request.
Normally, a disk responds to a write command with a queue full signal before the queue is completely full. Therefore, a disk can still receive some commands even after a queue full signal has been sent. However, problems occur when a disk is receiving commands faster than it can clear the queue. If the disk continues to receive commands after the occurrence of a queue full condition the queue can be exceeded and several commands can be sent and missed (e.g., silently dropped by the disk). In this event, the missed commands result in a timeout error being sent from the host bus adapter to the software disk driver.
In the peer-to-peer topology this problem has been easy to address. The simple solution for this situation is to limit the number of commands a device may send to the storage device to the maximum number of commands that the storage device can handle. For example, if the storage device has a queue depth of 64 commands, the computer may be limited to issuing no more than 64 commands at one time (e.g., no more than 64 commands may be pending). In this way the storage device's queue will never be exceeded.
In the arbitrated loop topology the problem is still relatively easy to solve by limiting the number of devices that may be on the loop and ha

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