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Red Hat ENTERPRISE LINUX 5.5 - ONLINE STORAGE GUIDE Manual

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Red Hat Enterprise
This document outlines the different procedures involved in reconfiguring storage devices while the
system is running. The document currently addresses iSCSI and Fibre Channel interconnects. Other
interconnects may be added in future versions of this document.
1. Introduction ............................................................................................................................. 2
1.1. Document Conventions ................................................................................................. 3
1.2. We Need Feedback! .................................................................................................... 5
2. Fibre Channel ......................................................................................................................... 6
2.1. Fibre Channel API ........................................................................................................ 6
2.2. Native Fibre Channel Drivers and Capabilities ............................................................... 7
3. iSCSI ..................................................................................................................................... 7
3.1. iSCSI API .................................................................................................................... 7
4. Persistent Naming ................................................................................................................... 8
4.1. WWID .......................................................................................................................... 9
4.2. UUID and Other Persistent Identifiers .......................................................................... 10
5. Removing a Storage Device .................................................................................................. 10
Linux 5.5
Online Storage Guide
For Red Hat Enterprise Linux 5
Red Hat Enterprise Linux Engineering
Mike Christie
Tom Coughlan
Don Domingo
Rob Evers
Development Community
Pasi Kärkkäinen
Abstract
1

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  Summary of Contents for Red Hat ENTERPRISE LINUX 5.5 - ONLINE STORAGE GUIDE

  • Page 1: Table Of Contents

    Red Hat Enterprise Linux 5.5 Online Storage Guide For Red Hat Enterprise Linux 5 Red Hat Enterprise Linux Engineering Mike Christie Tom Coughlan Don Domingo Rob Evers Development Community Pasi Kärkkäinen Abstract This document outlines the different procedures involved in reconfiguring storage devices while the system is running.
  • Page 2: Introduction

    Online Storage Guide 6. Removing a Path to a Storage Device ................... 12 7. Adding a Storage Device or Path ................... 12 8. Configuring a Fibre-Channel Over Ethernet Interface ............. 14 9. Scanning Storage Interconnects ..................... 14 10. iSCSI Discovery Configuration ..................... 15 11.
  • Page 3: Document Conventions

    Document Conventions Warning Online storage reconfiguration must be done carefully. System failures or interruptions during the process can lead to unexpected results. Red Hat advises that you reduce system load to the maximum extent possible during the change operations. This will reduce the chance of I/O errors, out-of-memory errors, or similar errors occurring in the midst of a configuration change.
  • Page 4 Online Storage Guide File-related classes include filesystem for file systems, file for files, and dir for directories. Each class has its own associated set of permissions. Proportional Bold This denotes words or phrases encountered on a system, including application names; dialog box text; labeled buttons;...
  • Page 5: We Need Feedback

    We Need Feedback! books Desktop documentation drafts photos stuff books_tests Desktop1 downloads images notes scripts svgs Source-code listings are also set in mono-spaced roman but add syntax highlighting as follows: package org.jboss.book.jca.ex1; import javax.naming.InitialContext; public class ExClient public static void main(String args[]) throws Exception...
  • Page 6: Fibre Channel

    Online Storage Guide When submitting a bug report, be sure to mention the manual's identifier: Online_Storage_Reconfiguration_Guide If you have a suggestion for improving the documentation, try to be as specific as possible when describing it. If you have found an error, please include the section number and some of the surrounding text so we can find it easily.
  • Page 7: Native Fibre Channel Drivers And Capabilities

    Native Fibre Channel Drivers and Capabilities Host: /sys/class/fc_host/hostH/ • port_id • issue_lip — instructs the driver to rediscover remote ports. 2.2. Native Fibre Channel Drivers and Capabilities Red Hat Enterprise Linux 5 ships with the following native fibre channel drivers: •...
  • Page 8: Persistent Naming

    Online Storage Guide This command displays the session/device state, session ID (sid), some negotiated parameters, and the SCSI devices accessible through the session. For shorter output (for example, to display only the sid-to-node mapping), run: iscsiadm -m session -P 0 iscsiadm -m session These commands print the list of running sessions with the format: driver [sid] target_ip:port,target_portal_group_tag proper_target_name...
  • Page 9: Wwid

    WWID For iSCSI devices, by-path/ names map from the target name and portal information to the sd name. It is generally not appropriate for applications to use these path-based names. This is because the storage device these paths reference may change, potentially causing incorrect data to be written to the device.
  • Page 10: Uuid And Other Persistent Identifiers

    Online Storage Guide \_ 6:0:0:1 sdf 8:80 [active][undef] Device-mapper-multipath automatically maintains the proper mapping of each WWID-based device name to its corresponding /dev/sd name on the system. These names are persistent across path changes, and they are consistent when accessing the device from different systems. When the user_friendly_names feature (of device-mapper-multipath) is used, the WWID is mapped to a name of the form /dev/mapper/mpathn.
  • Page 11 Removing a Storage Device (Section 4.1, below). If the device uses multipathing, then do this for the multipath "pseudo device" “WWID”) and each of the identifiers that represent a path to the device. If you are only removing a path to a multipath device, and other paths will remain, then the procedure is simpler, as described in Section 7, “Adding a Storage Device or Path”.
  • Page 12: Removing A Path To A Storage Device

    Online Storage Guide Procedure 1, “Ensuring a Clean Device Removal”, a device can be physically After performing removed safely from a running system. It is not necessary to stop I/O to other devices while doing so. Other procedures, such as the physical removal of the device, followed by a rescan of the SCSI bus Section 9, “Scanning Storage Interconnects”) to cause the operating system state to (as described in...
  • Page 13 Adding a Storage Device or Path the storage server. If this is not the case, note the World Wide Port Name (WWPN) for each port that will be used to access the new LUN. Next, make the operating system aware of the new storage device, or path to an existing device. The recommended command to use is: echo "c t l"...
  • Page 14: Configuring A Fibre-Channel Over Ethernet Interface

    Online Storage Guide 8. Configuring a Fibre-Channel Over Ethernet Interface Setting up and deploying a Fibre-channel over ethernet (FCoE) interface requires two packages: • fcoe-utils • dcbd Once these packages are installed, perform the following procedure to enable FCoE over a virtual LAN (VLAN): Procedure 3.
  • Page 15: Iscsi Discovery Configuration

    iSCSI Discovery Configuration Red Hat recommends that this type of scan be used only when necessary. In addition, the following restrictions must be observed when scanning storage interconnects: 1. All I/O on the effected interconnects must be paused and flushed before executing the procedure, and the results of the scan checked before I/O is resumed.
  • Page 16: Configuring Iscsi Offload And Interface Binding

    Online Storage Guide Node records in /var/lib/iscsi/nodes When logging into a target, iscsiadm uses the settings in this file. Discovery records in /var/lib/iscsi/discovery_type When performing discovery to the same destination, iscsiadm uses the settings in this file. Before using different settings for discovery, delete the current discovery records (i.e. /var/lib/ iscsi/discovery_type) first.
  • Page 17: Viewing Available Iface Configurations

    Viewing Available iface Configurations 11.1. Viewing Available iface Configurations Red Hat Enterprise Linux 5.5 supports iSCSI offload and interface binding for the following iSCSI initiator implementations: • Software iSCSI — like the scsi_tcp and ib_iser modules, this stack allocates an iSCSI host instance (i.e.
  • Page 18: Configuring An Iface For Software Iscsi

    Online Storage Guide iser iser,<empty>,<empty>,<empty>,<empty> cxgb3i.00:07:43:05:97:07 cxgb3i,00:07:43:05:97:07,<empty>,<empty>,<empty> It is also possible to display the settings of a specific iface configuration in a more friendly way. To do so, use the option -I iface_name. This will display the settings in the following format: iface.setting = value Using the previous example, the iface settings of the same Chelsio video card (i.e.
  • Page 19: Binding/Unbinding An Iface To A Portal

    Binding/Unbinding an iface to a Portal Before using the iface of a network card for iSCSI offload, first set the IP address (target_IP ) that the device should use. For ServerEngines devices that use the be2iscsi driver (i.e. ServerEngines iSCSI HBAs), the IP address is configured in the ServerEngines BIOS setup screen. For Chelsio and Broadcom devices, the procedure for configuring the IP address is the same as for any other iface setting.
  • Page 20: Scanning Iscsi Interconnects

    Online Storage Guide 12. Scanning iSCSI Interconnects For iSCSI, if the targets send an iSCSI async event indicating new storage is added, then the scan is done automatically. Cisco MDS™ and EMC Celerra™ support this feature. However, if the targets do not send an iSCSI async event, you need to manually scan them using the iscsiadm utility.
  • Page 21 Scanning iSCSI Interconnects You can also rescan a specific session by specifying the session's SID value, as in: iscsiadm -m session -r SID --rescan If your device supports multiple targets, you will need to issue a sendtargets command to the hosts to find new portals for each target.
  • Page 22: Logging In To An Iscsi Target

    Online Storage Guide iscsiadm --mode node --targetname proper_target_name --portal ip:port,target_portal_group_tag \ --login Using our previous example (where proper_target_name is equallogic-iscsi1), the full command would be: iscsiadm --mode node --targetname \ iqn.2001-05.com.equallogic:6-8a0900- ac3fe0101-63aff113e344a4a2-dl585-03-1 \ --portal 10.16.41.155:3260,0 -- login 13. Logging In to an iSCSI Target Section 3, “iSCSI”, the iSCSI service must be running in order to discover or log into As mentioned in...
  • Page 23: Resizing An Online Logical Unit

    Resizing an Online Logical Unit 14. Resizing an Online Logical Unit In most cases, fully resizing an online logical unit involves two things: resizing the logical unit itself and reflecting the size change in the corresponding multipath device (if multipathing is enabled on the system).
  • Page 24: Updating The Size Of Your Multipath Device

    Online Storage Guide • It re-scans for new/modified logical units the same way that the command echo 1 > / sys/block/sdX/device/rescan does. Note that this command is the same one used for re-scanning fibre-channel logical units. 14.3. Updating the Size of Your Multipath Device If multipathing is enabled on your system, you will also need to reflect the change in logical unit size to the logical unit's corresponding multipath device (after resizing the logical unit).
  • Page 25: Adding/Removing A Logical Unit Through Rescan-Scsi-Bus.sh

    Adding/Removing a Logical Unit Through rescan-scsi-bus.sh dmsetup suspend multipath_device Open the device mapper table you saved earlier (i.e. table_name). Change the second number (i.e. the disk end sector) to reflect the new number of 512 byte sectors in the disk. For example, if the new disk size is 2GB, change the second number to 4194304.
  • Page 26: Fibre Channel

    Online Storage Guide 16.1. Fibre Channel If a driver implements the Transport dev_loss_tmo callback, access attempts to a device through a link will be blocked when a transport problem is detected. To verify if a device is blocked, run the following command: cat /sys/block/device/device/state This command will return blocked if the device is blocked.
  • Page 27: Iscsi Settings With Dm-Multipath

    iSCSI Settings With dm-multipath it was originally removed. This can cause unexpected behavior when the device is added again. 16.2. iSCSI Settings With dm-multipath If dm-multipath is implemented, it is advisable to set iSCSI timers to immediately defer commands to the multipath layer. To configure this, nest the following line under device { in /etc/ multipath.conf: features "1 queue_if_no_path"...
  • Page 28: Iscsi Root

    Online Storage Guide To verify if the SCSI Error Handler is running, run: iscsiadm -m session -P 3 16.2.2. replacement_timeout replacement_timeout controls how long the iSCSI layer should wait for a timed-out path/session to reestablish itself before failing any commands on it. The default replacement_timeout value is 120 seconds.
  • Page 29: Controlling The Scsi Command Timer And Device Status

    Controlling the SCSI Command Timer and Device Status node.session.timeo.replacement_timeout = replacement_timeout After configuring /etc/iscsi/iscsid.conf, you must perform a re-discovery of the affected storage. This will allow the system to load and use any new values in /etc/iscsi/iscsid.conf. Section 12, “ Scanning iSCSI For more information on how to discover iSCSI devices, refer to Interconnects”.
  • Page 30: Troubleshooting

    Online Storage Guide cat /sys/block/device-name/device/state To set a device to running state, use: echo running > /sys/block/device-name/device/state Command Timer To control the command timer, you can write to /sys/block/device-name/device/timeout. To do so, run: echo value /sys/block/device-name/device/timeout Here, value is the timeout value (in seconds) you want to implement. Alternatively, you can also modify the timeout udev rule.
  • Page 31: Revision History

    Revision History This means that 3600d0230003414f30000203a7bc41a00 is mapped to two mpath links: dm-4 and dm-5. Next, open /etc/lvm/cache/.cache. Delete all lines containing stale-logical-unit and the mpath links that stale-logical-unit maps to. Using the same example in the previous step, the lines you need to delete are: /dev/dm-4 /dev/dm-5 /dev/mapper/3600d0230003414f30000203a7bc41a00...
  • Page 32 Online Storage Guide controlling SCSI command timer and device status Linux SCSI layer, 29 determining remote port states fibre channel modifying link loss behavior, 26 device status Linux SCSI layer, 29 devices, removing, 10 dev_loss_tmo fibre channel modifying link loss behavior, 26 fibre channel API, 6 dev_loss_tmo, changing fibre channel...
  • Page 33 Revision History native fibre channel drivers, 7 NOP-Out requests modifying link loss iSCSI configuration, 27 NOP-Outs (disabling) iSCSI configuration, 28 offline status Linux SCSI layer, 29 path to storage devices, adding, 12 path to storage devices, removing, 12 persistent naming, 8 port states (remote), determining fibre channel modifying link loss behavior, 26...
  • Page 34 Online Storage Guide Linux SCSI layer, 29 scanning storage interconnects, 14 SCSI command timer Linux SCSI layer, 30 SCSI Error Handler modifying link loss iSCSI configuration, 27 specific session timeouts, configuring iSCSI configuration, 29 storage interconnects, scanning, 14 symbolic links in /dev/disk persistent naming, 8 timeouts for a specific session, configuring iSCSI configuration, 29...