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https://www.howtoforge.com/replacing_hard_disks_in_a_raid1_array
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Note: If your RAID array is degraded you will see something like this
cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdb1[1] sda1[0](F)
487104 blocks super 1.2 [2/1] [_U]
md1 : active raid1 sdb2[1] sda2[0](F)
976142144 blocks super 1.2 [2/1] [_U]
== Get information about the hard drive(s) ==
sudo hdparm -I /dev/sda /dev/sda: HDIO_DRIVE_CMD(identify) failed: Input/output error
... and there is the failed hard drive ... fml. A healthy drive will show output similar to:
sudo hdparm -I /dev/sdb
/dev/sdb:
ATA device, with non-removable media
Model Number: WDC WD10EZEX-00WN4A0
Serial Number: WD-WCC6Y2ZHZJAH
Firmware Revision: 01.01A01
Transport: Serial, SATA 1.0a, SATA II Extensions, SATA Rev 2.5, SATA Rev 2.6, SATA Rev 3.0
Standards:
Used: unknown (minor revision code 0x001f)
Supported: 10 9 8 7 6 5
Likely used: 10
Configuration:
Logical max current
cylinders 16383 0
heads 16 0
sectors/track 63 0
--
LBA user addressable sectors: 268435455
LBA48 user addressable sectors: 1953525168
Logical Sector size: 512 bytes
Physical Sector size: 4096 bytes
device size with M = 1024*1024: 953869 MBytes
device size with M = 1000*1000: 1000204 MBytes (1000 GB)
cache/buffer size = unknown
Form Factor: 3.5 inch
Nominal Media Rotation Rate: 7200
Capabilities:
LBA, IORDY(can be disabled)
Queue depth: 32
Standby timer values: spec'd by Standard, with device specific minimum
R/W multiple sector transfer: Max = 16 Current = 16
DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 udma5 *udma6
Cycle time: min=120ns recommended=120ns
PIO: pio0 pio1 pio2 pio3 pio4
Cycle time: no flow control=120ns IORDY flow control=120ns
Commands/features:
Enabled Supported:
* SMART feature set
Security Mode feature set
* Power Management feature set
* Write cache
* Look-ahead
* Host Protected Area feature set
* WRITE_BUFFER command
* READ_BUFFER command
* NOP cmd
* DOWNLOAD_MICROCODE
Power-Up In Standby feature set
* SET_FEATURES required to spinup after power up
SET_MAX security extension
* 48-bit Address feature set
* Device Configuration Overlay feature set
* Mandatory FLUSH_CACHE
* FLUSH_CACHE_EXT
* SMART error logging
* SMART self-test
* General Purpose Logging feature set
* 64-bit World wide name
* {READ,WRITE}_DMA_EXT_GPL commands
* Segmented DOWNLOAD_MICROCODE
* Gen1 signaling speed (1.5Gb/s)
* Gen2 signaling speed (3.0Gb/s)
* Gen3 signaling speed (6.0Gb/s)
* Native Command Queueing (NCQ)
* Host-initiated interface power management
* Phy event counters
* NCQ priority information
* READ_LOG_DMA_EXT equivalent to READ_LOG_EXT
* DMA Setup Auto-Activate optimization
* Software settings preservation
* SMART Command Transport (SCT) feature set
* SCT Write Same (AC2)
* SCT Features Control (AC4)
* SCT Data Tables (AC5)
unknown 206[12] (vendor specific)
unknown 206[13] (vendor specific)
* DOWNLOAD MICROCODE DMA command
* WRITE BUFFER DMA command
* READ BUFFER DMA command
Security:
Master password revision code = 65534
supported
not enabled
not locked
frozen
not expired: security count
supported: enhanced erase
Logical Unit WWN Device Identifier: 50014ee20d232e87
NAA : 5
IEEE OUI : 0014ee
Unique ID : 20d232e87
Checksum: correct
or an alternative command
sudo lshw -class disk -class storage
... etc
*-scsi:0
physical id: 1
logical name: scsi0
capabilities: emulated
*-disk
description: SCSI Disk
physical id: 0.0.0
bus info: scsi@0:0.0.0
logical name: /dev/sda
size: 931GiB (1TB)
configuration: logicalsectorsize=512 sectorsize=512
*-scsi:1
physical id: 2
logical name: scsi1
capabilities: emulated
*-disk
description: ATA Disk
product: WDC WD10EZEX-00W
vendor: Western Digital
physical id: 0.0.0
bus info: scsi@1:0.0.0
logical name: /dev/sdb
version: 1A01
serial: WD-WCC6Y2ZHZJAH
size: 931GiB (1TB)
capabilities: partitioned partitioned:dos
configuration: ansiversion=5 logicalsectorsize=512 sectorsize=4096 signature=000e5fab
... etc
and another (possibly the best solution) program;
sudo smartctl -d ata -a -i /dev/sdb ... etc === START OF INFORMATION SECTION === Model Family: Western Digital Blue Device Model: WDC WD10EZEX-00WN4A0 Serial Number: WD-WCC6Y2ZHZJAH LU WWN Device Id: 5 0014ee 20d232e87 Firmware Version: 01.01A01 User Capacity: 1,000,204,886,016 bytes [1.00 TB] Sector Sizes: 512 bytes logical, 4096 bytes physical Rotation Rate: 7200 rpm Form Factor: 3.5 inches Device is: In smartctl database [for details use: -P show] ATA Version is: ACS-3 T13/2161-D revision 3b SATA Version is: SATA 3.1, 6.0 Gb/s (current: 6.0 Gb/s) Local Time is: Mon Jan 30 13:43:46 2017 EST SMART support is: Available - device has SMART capability. SMART support is: Enabled ... etc
== Remove the failed disk from the RAID1 array ==
In this example, I have 2 disks - /dev/sda and /dev/sdb with 2 partitions on each disk /dev/sda1, /dev/sda2, /dev/sdb1, /dev/sdb2 - and /dev/sda has died. Here is what mdstat looks like
mdadm --manage /dev/md0 --fail /dev/sda1 mdadm --manage /dev/md1 --fail /dev/sda2 mdadm --manage /dev/md0 --remove /dev/sda1 mdadm --manage /dev/md0 --remove /dev/sda2 shutdown -h now
- Physically remove the broken disk and install the new one
== Add the new disk to the RAID1 array ==
In this example, I have 2 disks - /dev/sda and /dev/sdb - and /dev/sda has died. Here is what mdstat looks like
cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md1 : active raid1 sdb2[1]
976142144 blocks super 1.2 [2/1] [_U]
md0 : active raid1 sdb1[1]
487104 blocks super 1.2 [2/1] [_U]
unused devices:
== Mirror the partitioning scheme from the RAID disk to the new disk ==
sfdisk -d /dev/sdb | sfdisk /dev/sda
== Add the new disk to the array ==
mdadm --manage /dev/md0 --add /dev/sda1 mdadm --manage /dev/md1 --add /dev/sda2
== Check the recovery status ==
cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md1 : active raid1 sda2[2] sdb2[1]
976142144 blocks super 1.2 [2/1] [_U]
[>....................] recovery = 0.3% (3282752/976142144) finish=103.7min speed=156321K/sec
md0 : active raid1 sda1[2] sdb1[1]
487104 blocks super 1.2 [2/2] [UU]
unused devices:
== Install GRUB to the MBR of the new disk ==
grub-install /dev/sda