Hi,
I'm using OMV 5.6.25-1.
Code
root@openmediavault:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid5 sdb[1] sda[4] sdd[5] sdc[2]
5860147200 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU]
bitmap: 0/15 pages [0KB], 65536KB chunk
unused devices: <none>
root@openmediavault:~# blkid
/dev/sda: UUID="e722afd9-5803-5460-ce00-e63017883000" UUID_SUB="acaec5ef-d304-a129-3754-9605267dcbdf" LABEL="openmediavault.local:zulu" TYPE="linux_raid_member"
/dev/sde1: UUID="173d1141-65e9-4ee1-ae31-b73d34f7b2cf" TYPE="ext4" PARTUUID="9d8e1096-01"
/dev/sde5: UUID="6947d5ca-f259-4fe7-be54-5b945620213c" TYPE="swap" PARTUUID="9d8e1096-05"
/dev/sdd: UUID="e722afd9-5803-5460-ce00-e63017883000" UUID_SUB="5eca6dcc-136e-506b-d09c-13fde444b570" LABEL="openmediavault.local:zulu" TYPE="linux_raid_member"
/dev/sdc: UUID="e722afd9-5803-5460-ce00-e63017883000" UUID_SUB="d49ed9a5-6400-f405-ea4d-0601f2e60642" LABEL="openmediavault.local:zulu" TYPE="linux_raid_member"
/dev/sdb: UUID="e722afd9-5803-5460-ce00-e63017883000" UUID_SUB="5667c0d5-4cec-a644-36a3-e641ec176a46" LABEL="openmediavault.local:zulu" TYPE="linux_raid_member"
/dev/sdf1: LABEL="Backup" UUID="83ed8d9d-e2f7-4e64-bfc8-8fe26f404112" TYPE="ext4" PARTUUID="4f80a638-fd4a-44e9-851a-3c9575507f12"
/dev/md0: LABEL="zulu" UUID="4c0e7ba7-40f6-47cc-86e6-75faeccc7212" TYPE="ext4"
root@openmediavault:~# fdisk -l | grep "Disk "
Disk /dev/sda: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Disk model: TOSHIBA HDWD120
Disk /dev/sde: 111.8 GiB, 120034123776 bytes, 234441648 sectors
Disk model: CT120BX500SSD1
Disk identifier: 0x9d8e1096
Disk /dev/sdd: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Disk model: TOSHIBA HDWD120
Disk /dev/sdc: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Disk model: SAMSUNG HD204UI
Disk /dev/sdb: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Disk model: Hitachi HDS72302
Disk /dev/sdf: 5.5 TiB, 6001175125504 bytes, 11721045167 sectors
Disk model: Expansion Desk
Disk identifier: B27D326A-00A1-47B0-B2D5-732A08CA3BEA
Disk /dev/md0: 5.5 TiB, 6000790732800 bytes, 11720294400 sectors
root@openmediavault:~# cat /etc/mdadm/mdadm.conf
# This file is auto-generated by openmediavault (https://www.openmediavault.org)
# WARNING: Do not edit this file, your changes will get lost.
# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#
# by default, scan all partitions (/proc/partitions) for MD superblocks.
# alternatively, specify devices to scan, using wildcards if desired.
# Note, if no DEVICE line is present, then "DEVICE partitions" is assumed.
# To avoid the auto-assembly of RAID devices a pattern that CAN'T match is
# used if no RAID devices are configured.
DEVICE partitions
# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes
# automatically tag new arrays as belonging to the local system
HOMEHOST <system>
# instruct the monitoring daemon where to send mail alerts
MAILADDR omvnotifications@xx.co.uk
MAILFROM root
# definitions of existing MD arrays
ARRAY /dev/md0 metadata=1.2 name=openmediavault.local:zulu UUID=e722afd9:58035460:ce00e630:17883000
root@openmediavault:~# mdadm --detail --scan --verbose
ARRAY /dev/md0 level=raid5 num-devices=4 metadata=1.2 name=openmediavault.local:zulu UUID=e722afd9:58035460:ce00e630:17883000
devices=/dev/sda,/dev/sdb,/dev/sdc,/dev/sdd
root@openmediavault:~# One of my RAID 5 disks is showing "Pre-fail" in the SMART Test and I'd like to replace it.
I have asked about this before and in my notes I have: "If the drive was showing errors and needed replacing, then Raid Management -> select the raid then click delete on the menu, select the drive click OK and the drive is removed, then proceed to add the new drive. All this can be done via the WebUI and no command line necessary."
My problem is that "Delete" button isn't available. See attachment.
What am I doing wrong? How do I replace the disk? 
I assume there's a difference between "Remove" and "Delete"...?
Thanks!
S
