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 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 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 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 get the UUID of the disk:

blkid

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 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

Subvolumes can be mounted like separate filesystems

mount -o subvol=/oldpath /dev/sda5 /newpath

so the subvolume is now also visible under newpath

See also here

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 [email protected]

Scan for devices:

smartctl --scan

Show detailed information about a device:

smartctl --all /dev/sda