View source for Linux - Disks and Filesystems


== iSCSI ==

* Block storage provider: iSCSI Target
* Storage client: iSCSI Initiator
* Dynamic Discovery: Initiator sends  'SendTargets' request to a single IP/port and if the target listens on multiple names and addresses, all of them are sent in a form of TargetName and TargetAddress (IP:port#).
* See [https://en.wikipedia.org/wiki/ISCSI here] for background and IQN naming.

=== Target ===

* Install package (and dependencies: targetcli
* Choose/create local area for disk images: /iscsi_disks

Start admin utility:
 targetcli
 /> cd /backstores/fileio
 /backstores/fileio> create disk01 /iscsi_disks/disk01.img 10G
 /backstores/fileio> cd /iscsi
 /iscsi> create iqn.2000-01.com.example:storage.target01
 /iscsi> cd iqn.2000-01.com.example:storage.target01/tpg1/luns
 /iscsi/iqn.20...t01/tpg1/luns> create /backstores/fileio/disk01
 /iscsi/iqn.20...t00/tpg1/luns> cd ../acls
 /iscsi/iqn.20...t00/tpg1/acls> create iqn.2000-01.com.example:initiator01
 /iscsi/iqn.20...t00/tpg1/acls> cd iqn.2000-01.com.example:initiator01
 /iscsi/iqn.20...an-server01> set auth userid=someuser
 /iscsi/iqn.20...an-server01> set auth password=somepass
 exit

Other commands within targetcli:
 ls
 delete [object]
 help

 systemctl enable target
 systemctl start target

If necessary, open firewall for 3260:
 firewall-cmd --add-service=iscsi-target --permanent
 firewall-cmd --reload

See also [https://www.lisenet.com/2016/iscsi-target-and-initiator-configuration-on-rhel-7/ here]

=== Initiator ===

Install package: iscsi-initiator-utils

In /etc/iscsi/initiatorname.iscsi specify the iSCSI target:
 InitiatorName=iqn.2000-01.com.example:initiator01

In /etc/iscsi/iscsid.conf:
 node.session.auth.authmethod = CHAP
 node.session.auth.username = username
 node.session.auth.password = password

Discover target:
 # iscsiadm -m discovery -t sendtargets -p san-server01
 san-server01:3260,1 iqn.2000-01.com.example:storage.target01

More info:
 iscsiadm -m node -o show
 ...

Login:
 iscsiadm -m node --login

Confirm session:
 iscsiadm -m session -o show

Confirm new device added (eg sdc):
 cat /proc/partitions

Then, partition, format and mount /dev/sdc as normal.

Logout of iSCSI (after unmounting used filesystems):
 iscsiadm -m node --logout

== Disk Management ==

=== Grub ===

When installing on a RAID 1 mirror for the OS grub boot loader only installs on the first disk, so it that fails you can't boot off the second. To copy loader to the second disk:

 grub> find /grub/stage1

This should find (hd0,0) and (hd1,0) which correspond for /dev/sda and /dev/sdb. Then temporarily make sdb the first disk and install:

 device (hd0) /dev/sdb
 root (hd0,0)
 setup (hd0)

=== HD Parameters ===

Show settings/features:
 hdparm -I /dev/sda

Test transfer rate:
 hdparm -t --direct /dev/sda

Show power management setting:
 hdparm -B /dev/sda

=== MD RAIDs ===

Create an array of 2 disks in a RAID1 (mirror):
 mdadm --create /dev/md0 -l 1 -n 2 /dev/sdb1 /dev/sdc1

Monitor status with:
 mdadm --detail /dev/md0
 cat /proc/mdstat

Ensure RAID is detected at boot time:
 mdadm -Es >> /etc/mdadm.conf

Remove a device from an array:
 mdadm --remove /dev/md0 /dev/sdb1

Fail a drive in an array:
 mdadm --fail /dev/md0 /dev/sdb1

Add a device to an array:
 mdadm --add /dev/md0 /dev/sdb1

The /etc/cron.weekly/99-raid-check script can sometimes report:
 WARNING: mismatch_cnt is not 0 on /dev/md1

The actual mismatch count can be found:
 cat /sys/block/md1/md/mismatch_cnt

A repair and rebuild can be:
 echo repair > /sys/block/md1/md/sync_action
 echo check > /sys/block/md1/md/sync_action

=== Partitioning ===

==== FDisk ====

Supports MBR partitions

==== Parted ====

Supports MBR and GPT

See [https://www.gnu.org/software/parted/manual/html_chapter/parted_2.html#SEC8 Manual]

=== LVM ===

==== Physical Volumes ====

To create a PV out of two partions:
 pvcreate /dev/sdc1 /dev/sdd1

To show current PVs:
 pvscan

==== Volume Groups ====

To create a VG:
 vgcreate vg00 /dev/sd[cd]

To show all current VGs:
 vgscan

To show details of a VG (including free PEs):
 vgdisplay vg00

To extend a volume group by adding a new PV:
 vgextend vg00 /dev/sde

To make a volume group available:
 vgchange -ay vg00

==== Logical Volumes ====

To create a new LV:
 lvcreate --size 100M vg00 -n lv00
or change --size option to --extents 500 or --extents 60%VG or -l 100%FREE  

eg to create a RAID5 array out of 3 disks (2 data):
 lvcreate -n lv00 --type raid5 -i 2 --extents 100%FREE vg00

Show status of LVM RAID:
 lvs -a vg00

To rename a LV in VG vg01:
 lvrename vg00 lvold lvnew

To remove a LV:
 lvremove vg00/lv01

To show current LVs:
 lvscan

== Filesystems ==

To format with 1% minfree, large file support (see types in /etc/mke2fs.conf), journalling and a label:
 mkfs.ext4 -m 1 -T largefile4 -j -L /home /dev/mapper/vg00-lv00

To alter the label:
 e2label /dev/sda newlabel

To mount at boot time, enter in
* /etc/fstab

Or to use XFS on a LV:
 mkfs.xfs -L /home /dev/mapper/vg0-lv0

== BTRFS ==

See also [https://btrfs.wiki.kernel.org/index.php/SysadminGuide here]

Create a RAID5 array for data and metadata:
 mkfs.btrfs -L data -d raid5 -m raid5 -f /dev/sdc /dev/sdd /dev/sde

View usage:
 btrfs filesystem usage /data

Look for btrfs filesystems:
 blkid --match-token TYPE=btrfs

=== Subvolumes ===

Create subvolume:
  btrfs subvolume create /data/db

Info:
 btrfs subvolume list .
 btrfs subvolume list /data
 btrfs subvolume show /data/db

Delete subvolume:
  btrfs subvolume delete /data/db

=== Compression ===

Mount with compression option in fstab:
 compress=zstd:1
where the algorirm could also be lzo or zlib. Compression level can be increased to 2 or 3

Per-file/directory/subvolume compression is also available:
 btrfs property get /somefile compression
 btrfs property set /etc compression zlib

Degragment:
  btrfs filesystem defragment -r /

== Loopback Filesystem ==

 dd if=/dev/zero of=loopback.img bs=1024M count=5
 losetup -fP loopback.img

To show loopback device(s):
 losetup -a
 losetup -l

To delete loopback device:
 losetup -d /dev/loop0

Then, create filesystem, eg:
 mkfs.xfs -L backups loopback.img

And mount /dev/loop0 (-o loop) as a traditional device. Note: the losetup configuration is lost at restart so can't be added to /etc/fstab for at-boot mounting.

== Smarttools ==

/etc/smartmontools/smartd.conf

Default to scan ATA/SCSI devices and report problems to root:
 DEVICESCAN -H -m root -M exec /usr/libexec/smartmontools/smartdnotify -n standby,10,q

Or a specific device, and email an external user:
 /dev/sda -a -o on -S on -s (S/../.././02|L/../../6/03) -m user@domain.com

Scan for devices:
 smartctl --scan

Show detailed information about a device:
 smartctl --all /dev/sda