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| '''This is a WIP'''
| | #REDIRECT [[Linux iSCSI Target (TCM)]] |
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| == Introduction ==
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| This HOW-TO is focusing on performance. This is why I made some decisions targeted on performance instead of security (like you are used in Alpine Linux).
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| This means we are not using grsec and not using a firewall. I presume you will take security actions on another level.
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| To get started, you can download a boot cd here:
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| http://alpine.nethq.org/distfiles/alpine-scst-110106-x86_64.iso
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| == Content ==
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| * Vanilla kernel with SCST (linux-scst)
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| * Linux software raid and raid level (mdadm)
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| * Volume Management (LVM2)
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| * SCST administration (scstadmin)
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| * Linux raid monitoring
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| == Vanilla Linux kernel with SCST patches ==
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| The default Linux kernel will provide support for iSCSI. The biggest issues with this implementation is it operates in userspace. SCST iSCSI will run in kernel and this is one of the reasons why it preforms much better. SCST performance depends on specific patches which need to be applied to the kernel. This is why we created a separate kernel just for SCST usage. SCST modules are already included by default so there is no need for a separate module package to be installed.
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| P.S. We only provide an x86_64 kernel for SCST because it will perform better on 64bit systems.
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| == Linux software raid ==
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| In my personal setup i have 4 pieces of WD RE4 1TB drives which i want to use in the best performance raid level with redundancy.
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| According to many mailing lists and opinion of the Linux raid author RAID10 with layout f2 (far) seems to preform best while still having redundancy.
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| Please remember with RAID10 50% of your hard disk space will go to redundancy, but performance is almost the same as RAID0 (stripe).
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| For most up-to-date information regarding Linux software raid: https://raid.wiki.kernel.org/index.php/Overview
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| RAID10 has multiple layout types. f(far)2 in tests seem to preform the best. Please see above link for references.
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| mdadm -v --create /dev/md0 --level=raid10 --layout=f2 --raid-devices=4 /dev/sda /dev/sdb /dev/sdc /dev/sdd
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| I am not using partitions on my disks, although there are reasons to use partitions, see here:
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| https://raid.wiki.kernel.org/index.php/Partition_Types
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| You can now monitor your raid (re)building: cat /proc/mdstat
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| By default, the rebuild speed will be set and can be checked and changed here:
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| cat /proc/sys/dev/raid/speed_limit_max
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| cat /proc/sys/dev/raid/speed_limit_min
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| make sure we have raid10 module loaded at boot
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| echo raid10 >> /etc/modules
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| When you are happy with your raid configuration, save its information to mdamd.conf file
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| mdadm --detail --scan >> /etc/mdadm.conf
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| It should display something like
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| ARRAY /dev/md0 metadata=1.2 name=scst:0 UUID=71fc93b8:3fef0057:9f5feec1:7d9e57e8
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| When you are ready with your raid setup and its functioning, you will need to make sure its starting at boot time
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| rc-update add mdadm-raid default
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| == Monitor software raid ==
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| Linux software raid can be monitored with mdadm daemon option. Alpine Linux includes an initd script which can invoke the daemon | |
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| /etc/init.d/mdadm
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| It will be default monitor the array's defined in mdadm.conf. To receive email notifications about array issues, we need to provide our email address inside mdadm.conf:
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| MAILADDR me@inter.net
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| Because mdadm cannot send email itself, we need to setup an sendmail (replacement) program.
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| apk add ssmtp
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| Ssmtp can be configured by editing /etc/ssmtp/ssmtp.conf
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| You can monitor messages (syslog) for actions invoked by mmdadm.
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| If you have your own monitoring system active, you can also let mdadm issue a script and notify it.
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| == SCST and iSCSI management ==
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| When starting with SCST management we need to have the SCST framework (kernel module) and the iSCSI kernel module loaded
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| modprobe scst scst_vdisk iscsi_scst
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| After these are loaded we can start the iSCSI deamon
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| /etc/init.d/iscsi-scst start
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| This command will return some information based on the current configuration located in: /etc/scst.conf
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| The basic config when only having iSCSI loaded is:
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| TARGET_DRIVER iscsi {
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| enabled 0
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| }
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| We start add adding a target to the correct target driver
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| scstadmin -add_target iqn.2010-12.org.alpinelinux:tgt -driver iscsi
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| The config at this point should be:
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| TARGET_DRIVER iscsi {
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| enabled 0
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| TARGET iqn.2010-12.org.alpinelinux:tgt {
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| enabled 0
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| }
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| }
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| Now that we have a target in our configuration we need to add a device:
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| scstadmin -open_dev disk01 -handler vdisk_fileio -attributes filename=/mnt/array1/disk01,nv_cache=1
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| HANDLER vdisk_fileio {
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| DEVICE disk01 {
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| t10_dev_id "disk01 b8ceed65"
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| usn b8ceed65
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|
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| filename /mnt/array1/disk01
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| nv_cache 1
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| }
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| }
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| TARGET_DRIVER iscsi {
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| enabled 0
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| TARGET iqn.2010-12.org.alpinelinux:tgt {
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| enabled 0
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| }
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| }
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| To add the device to the target we need to specify which LUN it will be. (we always need to start with 0)
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| scstadmin -add_lun 0 -driver iscsi -target iqn.2010-12.org.alpinelinux:tgt -device disk01
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| HANDLER vdisk_fileio {
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| DEVICE disk01 {
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| t10_dev_id "disk01 b8ceed65"
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| usn b8ceed65
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|
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| filename /mnt/array1/disk01
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| nv_cache 1
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| }
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| }
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| TARGET_DRIVER iscsi {
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| enabled 0
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| TARGET iqn.2010-12.org.alpinelinux:tgt {
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| enabled 0
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| LUN 0 disk01
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| }
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| }
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| To close a device
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| scstadmin -close_dev disk01 -handler vdisk_fileio
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