RAID Storage Redundancy

Linux

Storage

Published

August 27, 2013

Modified

September 14, 2023

Overview

RAID (Redundant Array of Inexpensive/Independent Disks)…

…dedicated hardware controller or entirely in software
RAID system will have several storage devices as the bottom layer
- …these will be partitioned (another block device)…
- …and combined into a raid array (yet another block device)

Reasons to use RAID…

Performance…
- …enhanced transfer speed
- …enhanced number of transactions per second
- …increased single block device capacity
Redundancy…
- …greater efficiency in recovering from a device failures
- Should never be used as a replacement for reliable backup

Types & Levels

Three possible types of RAID…

Firmware RAID…onboard integrated RAID controllers
Hardware RAID…dedicated RAID controller (typically PCIe)
Software RAID…completely hardware independent

Standard numbering system of raid levels…

RAID without redundancy…

Linear - Simple grouping of drive…
- …creates a larger virtual drive…
- ..called append mode…IO to one device until full
RAID 0 - Striping
- …data is interleaved across all drives in the array
- Bottlenecks associated with I/O to a single device are alleviated
JBOD (Just a Bunch Of Disks)
- …circumvent RAID firmware…act like a normal disk controller
- configure device without RAID support

RAID with redundancy…

RAID 1 - Mirroring
- …exact replica of all data on all devices
- Write performance hit…increases with number of devices
RAID 4 - Dedicated Parity (…obsolete)
- …dedicated drive is used to store parity
- Single device failure can be recovered
RAID 5 - Distributed Parity (block-level striping)
- At least 3 devices…support one device failure
- …parity information is spread across all devices
- Reduce the bottleneck inherent in writing parity
RAID 6 - Double Distributed Parity
- At least 4 devices…supports two device failures
- Write speed is slow because of double parity…restoring process is long

Nested RAIDs..

RAID 10 - Striping Mirror
- …hybrid array results from the combination of RAID-0 and RAID-1
- Performance of striping…redundant properties of mirroring
- …most expensive solution…lot of surplus disk hardware
RAID 50 - Striping Parity
- …combine two RAID-5 arrays into a striped array
- Performance is slightly lower than a RAID 10
- Each RAID-5 can survive a single disk failure

RAID storage capacities…

RAID level	Realized capacity
Linear mode	DiskSize 0+ DiskSize 1 +…DiskSizen
RAID-0 (striping)	TotalDisks * DiskSize
RAID-1 (mirroring)	DiskSize
RAID-4,5,6	(TotalDisks-1) * DiskSize
RAID-10 (striped mirror)	NumberOfMirrors * DiskSize
RAID-50 (striped parity)	(TotalDisks-ParityDisks) * DiskSize

Terminology

Parity algorithms are an alternative to mirroring for redundancy…
Striping…data is spread across multiple disks
- …improves read and write performance
- …stripes also support redundancy through disk parity
Degraded…array supporting redundancy…with a failed device
Rebuild (aka recovery)…
- ..reconstructed using the parity information provided by the remaining disks
- Usually puts an additional strain on system resource
Scrubbing…check for data corruption and errors…

Automation to using a spare device…

Hot-Spare
- Extra storage devices to act as spares when a drive failure occurs
- …replace a failed drive with a new drive without intervention
- Decreases the chance that a second drive will fail and cause data loss
Hot-Swap
- Removed a failed drive from a running system…without reboot
- Need special hardware that supports it…mostly available today…

`mdadm`

Linux Software RAID…

mdraid subsystem was designed as a software RAID solution for Linux
- Package mdadm*.{deb,rpm}…configured with the mdadm utility
- Can consists of…
  - …physical devices
  - …partitions
  - …any Linux block device
dmraid (deprecated) used on a wide variety of firmware RAID implementations
Hardware RAID controllers have no specific RAID subsystem…
- …come with their own drivers…
- …allow the system to detect the RAID sets as regular disks

Terminology…

Superblock contains RAID metadata…
- ~1KB stored in the beginning or in the end of each member disk
- RAID information…same on all the disks
  - Number of devices…block size
  - RAID level and layout
- Disk information…unique to each disk
  - Superblock number…
  - Disk role…column height
- …allows the array to be reliably re-assembled after a shutdown
Assemble…rebuilds all RAID arrays
- mdadm --assemble --scan…scan drives for superblocks
- partially assembled array…in case of issues
- …automatic during boot…create mdadm.conf
- …requires support in initramfs if used for / (root-partition)
Scrubbing…
- …regularly read blocks on devices to catch bad blocks early
- …read-error handling…write back of correct data from other devices
- …blocks read successfully…found to not be consistent…mismatch

`/dev/md*`

md multiple device driver…man 4 md

RAID solution that is completely hardware independent…
- …implements the various RAID levels in the kernel disk (block device) code
- …dependent on the server CPU performance and load
/dev/md* virtual devices…created from one or more independent underlying devices

Basic command syntax…

mdadm [mode] <raid-device> [options] <component-devices>

`mdadm.conf`

Configuration file…

…collection of words separated by white space… # for comments
Keywords…
- DEVICE list devices/partitions t- ARRAY identify arrays for assembly
- MAIL{ADDR,FORM} configure alert mail notification
- CREATE default for array creation
- …more cf. man 5 mdadm.conf

# add a configuration to the end
mdadm --detail --scan >> /etc/mdadm.conf

ARRAY example configuration…

ARRAY /dev/md0 metadata=1.2 name=node.fqdn:0 UUID=42650a5c:7eb06556:6db9f264:03ec67e8

…second word /dev/md* device to assembled…or ignore
otherwise…use various heuristics to determine an appropriate name
…subsequent words identify the array,
- name identifier…typically the node name with device number as suffix
- uuid 128 bit…stored in the superblock
- devices…comma separated list of device names

Create

Create a RAID configuration…mode --create

…writes the per-device superblocks…initialisation…
- …making sure disks of a mirror are identical
- or…parity array the parities are correct
-–level= RAID level…
–raid-devices= number of active devices in the array

# mirror
mdadm --create /dev/md0 --level=raid1 --raid-devices=2 /dev/nvme[0-1]n1
# parity raid
mdadm --create /dev/md0 --level=raid5 --raid-devices=3 /dev/sd[abc]3

Monitor

# inspect the configuration in detail
mdadm --detail /dev/md0
# detailed information about each RAID device
mdadm --examine /dev/sd[bc]1

/proc/mdstat snapshot of the kernel’s RAID/md state…

watch -n .1 cat /proc/mdstat
# ...more details...
mdadm --misc --detail /dev/md[012]

Manage

Remove device from array…

--fail if not already in failed stated (due to a defect)
--remove a device from an array

mdadm /dev/md0 --fail /dev/sda1 --remove /dev/sda1

--add new device to array (replacing a failed one probably)

mdadm --add /dev/md0 /dev/sdb1

Stop and delete array…

# unmount the file-systems...
umount /dev/md0
# stop the device...
mdadm --stop /dev/md0
# remove the device
mdadm --remove /dev/md0
# ...incase if it errors with "No such file or directory"
mdadm --zero-superblock /dev/sda1 /dev/sdb1

`dm-raid`

Device-mapper RAID (dm-raid) target provides a bridge from DM to MD…

…allows the mdraid drivers to be accessed using a device-mapper interface
Supports…
- …RAID device discovery
- …RAID set activation, creation, removal, rebuild
- …display of properties for ATARAID/DDF1 metadata

`lvm` RAID

LVM supports RAID…

…created and managed by LVM using the mdraid kernel drivers
…levels 0, 1, 4, 5, 6, and 10
Supports snapshots…

Create a RAID logical volume using lvcreate

lvcreate --type raid1 -m 1 -L 1G -n my_lv my_vg

ZFS

Implements RAID-Z…

…variation on standard RAID-5 that offers better distribution of parity
Eliminates RAID-5 write hole…inconsistency in case of power loss
Three levels…
- …based on the number of parity devices
- …number of disks that can fail while the pool remains operational

Pool type in order of performance…

mirror – More disks, more reliability, same capacity. (RAID 1)
raidz1 – Single parity, minimum 3 disks. Two disk failures results in data loss.
raidz2 – Dual parity, minimum 4 disks. Allows for two disk failures.
raidz3 – Triple parity, minimum 5 disks. Allows for three disk failures.

zfs list [<name>]                      # show file-systems
zfs set mountpoint=<path> <name>       # set target mount point for file-system 
zfs mount <name>                       # mount a file-system
zfs umount <path>                      # unmount a file-system
grep -i mount= /etc/default/zfs        # boot persistance
findmnt -t zfs                         # list mounted file-systems
zfs list -o quota <name>               # show quota for file-system
zfs set quota=<size> <name>            # set quota for file-system
zpool status [<name>]                  # show storage pools
zpool scrub <name>                     
zpool create <name> <type> <device> [<device>,...]
                                       # create a new storage pool

Btrfs

…ability to combine and manage several disks as one filesystem

Supports following RAID profiles…

RAID 1…
- RAID 1c3…stores 3 copies on separate disk
- RAID 1c4…stores 4 copies on separate disks
RAID 10…RAID1+RAID0 modes for increased performance and redundancy
…not yet stable or suitable for production use
- RAID 5…striped mode with 1 disk as redundancy
- RAID 6…striped mode with 2 disks as redundancy

`storecli`

lspci | grep -i raid           # find hardware RAID controllers

MegaRAID SAS is the current high-end RAID controllers series by LSI

StorCLI Reference Manual
Search for the latest version on the Broadcom web-page.
- Download will require accepting EULA…
- unzip the archive
- Add the noarch to the repository

# list the included packages...
>>> find Unified_storcli_all_os -name '*.rpm'
Unified_storcli_all_os/ARM/Linux/storcli-007.2007.0000.0000-1.aarch64.rpm
Unified_storcli_all_os/Linux/storcli-007.2007.0000.0000-1.noarch.rpm
# ...install the command-line tools
>>> dnf install -y Unified_storcli_all_os/Linux/storcli-007.2007.0000.0000-1.noarch.rpm
# for simplicity...
>>> ln -s /opt/MegaRAID/storcli/storcli64 /sbin/storcli

storcli command interfaces with the RAID controller…following general format…

<[object identifier]> <verb> <[adverb | attributes | properties] > <[key=value]>

Object identifiers…
- /cx controller x
- /cx/vx virtual drive x on controller x
Verbs… add, del, set, show, etc.
<[adverb | attributes | properties] >…
- …specifies what the verb modifies or displays
- <[key=value]> …if a value is required by the command

# summary of the drive and controller status
storcli show
# number of controllers detected
storcli show ctrlcount 
# show controller specifics...
storcli /c0 show | grep -e ^Product -e ^Serial -e Version
# ...controller & virtual devices configuration
storcli /c0/v0 show all

Devices

Show the list of devices on a specific controller…

EID:Slt enclosure number and slot numbers

# ...first controller in this example
>>> storcli /c0 show
...
---------------------------------------------------------------------------------
EID:Slt DID State DG       Size Intf Med SED PI SeSz Model               Sp Type 
---------------------------------------------------------------------------------
8:0       9 Onln   0 446.625 GB SATA SSD N   N  512B INTEL SSDSC2KG480G8 U  -    
8:1      10 Onln   0 446.625 GB SATA SSD N   N  512B INTEL SSDSC2KG480G8 U  -    
8:2      16 Onln   1   5.457 TB SAS  HDD N   N  512B HUS726060AL5210     U  -    
8:3      11 Onln   1   5.457 TB SAS  HDD N   N  512B HUS726060AL5210     U  -    
8:4      12 Onln   1   5.457 TB SAS  HDD N   N  512B HUS726060AL5210     U  -    
8:5      13 Onln   1   5.457 TB SAS  HDD N   N  512B HUS726060AL5210     U  -    
8:6      14 Onln   1   5.457 TB SAS  HDD N   N  512B HUS726060AL5210     U  -    
8:7      15 Onln   1   5.457 TB SAS  HDD N   N  512B HUS726060AL5210     U  -    
---------------------------------------------------------------------------------
...

Configuration

Create add vd RAID configuration, aka virtual drive…

r6 aka type=raid6
drives=e:s|e:s-x|e:s-x,y
- e specifies the enclosure ID, s represents the slot
- e:s-x range convention…slots s to x in the enclosure e
AWB (always write back) ignores the non-existence of a cache module
ra read ahead should be helpful if the read access is fairly regular
Strip=64 is believed to by a potentially important parameter…
- …amount of data written to one physical disk before moving to the next one…
- …in reality no one knows about the I/O, so take some middle value here

# created a Raid array
storcli /c0 add vd r6 drives=8:2-7 AWB ra cached Strip=64

Sanity Checks

Basic sanity checks are enable for the RAID controller:

Patrol read checks all disks for bad blocks…
- …if the system load is small
- …should not have a noticeable performance impact
Consistency check for parity…time interval delay=2016 (roughly 3 month)

# run both consistency checks and patrol reads
storcli /c0 set cc=conc delay=2016 starttime=2022/04/28 11

--- title: RAID Storage Redundancy categories: - Linux - Storage date: 2013/08/27 date-modified: 2023/09/14 toc-expand: 3 --- ## Overview RAID (Redundant Array of Inexpensive/Independent Disks)... - ...dedicated hardware controller or entirely in software - RAID system will have several storage devices as the bottom layer - ...these will be partitioned (another block device)... - ...and combined into a raid array (yet another block device) Reasons to use RAID... - **Performance**... - ...enhanced transfer speed - ...enhanced number of transactions per second - ...increased single block device capacity - **Redundancy**... - ...greater efficiency in recovering from a device failures - Should never be used as a replacement for reliable backup ## Types & Levels Three possible **types** of RAID... - Firmware RAID...onboard integrated RAID controllers - Hardware RAID...dedicated RAID controller (typically PCIe) - Software RAID...completely hardware independent Standard numbering system of **raid levels**... RAID without redundancy... - Linear - Simple grouping of drive... - ...creates a larger virtual drive... - ..called append mode...IO to one device until full - RAID 0 - Striping - ...data is interleaved across all drives in the array - Bottlenecks associated with I/O to a single device are alleviated - JBOD (Just a Bunch Of Disks) - ...circumvent RAID firmware...act like a normal disk controller - configure device without RAID support RAID with redundancy... - **RAID 1** - Mirroring - ...exact replica of all data on all devices - Write performance hit...increases with number of devices - RAID 4 - Dedicated Parity (...obsolete) - ...dedicated drive is used to store parity - Single device failure can be recovered - RAID 5 - Distributed Parity (block-level striping) - At least 3 devices...support one device failure - ...parity information is spread across all devices - Reduce the bottleneck inherent in writing parity - **RAID 6** - Double Distributed Parity - At least 4 devices...supports two device failures - Write speed is slow because of double parity...restoring process is long Nested RAIDs.. - **RAID 10** - Striping Mirror - ...hybrid array results from the combination of RAID-0 and RAID-1 - Performance of striping...redundant properties of mirroring - ...most expensive solution...lot of surplus disk hardware - RAID 50 - Striping Parity - ...combine two RAID-5 arrays into a striped array - Performance is slightly lower than a RAID 10 - Each RAID-5 can survive a single disk failure RAID storage capacities... RAID level | Realized capacity ---------------------------|------------------------- Linear mode | DiskSize 0+ DiskSize 1 +...DiskSizen RAID-0 (striping) | TotalDisks * DiskSize RAID-1 (mirroring) | DiskSize RAID-4,5,6 | (TotalDisks-1) * DiskSize RAID-10 (striped mirror) | NumberOfMirrors * DiskSize RAID-50 (striped parity) | (TotalDisks-ParityDisks) * DiskSize ## Terminology - **Parity** algorithms are an alternative to mirroring for redundancy... - **Striping**...data is spread across multiple disks - ...improves read and write performance - ...stripes also support redundancy through disk parity - **Degraded**...array supporting redundancy...with a failed device - **Rebuild** (aka recovery)... - ..reconstructed using the parity information provided by the remaining disks - Usually puts an additional strain on system resource - **Scrubbing**...check for data corruption and errors... Automation to using a spare device... - **Hot-Spare** - Extra storage devices to act as spares when a drive failure occurs - ...replace a failed drive with a new drive without intervention - Decreases the chance that a second drive will fail and cause data loss - **Hot-Swap** - Removed a failed drive from a running system...without reboot - Need special hardware that supports it...mostly available today... ## `mdadm` Linux Software RAID... - `mdraid` subsystem was designed as a software RAID solution for Linux - Package `mdadm*.{deb,rpm}`...configured with the `mdadm` utility - Can consists of... - ...physical devices - ...partitions - ...any Linux block device - `dmraid` (deprecated) used on a wide variety of firmware RAID implementations - Hardware RAID controllers have no specific RAID subsystem... - ...come with their own drivers... - ...allow the system to detect the RAID sets as regular disks Terminology... - **Superblock** contains RAID metadata... - ~1KB stored in the beginning or in the end of each member disk - RAID information...same on all the disks - Number of devices...block size - RAID level and layout - Disk information...unique to each disk - Superblock number... - Disk role...column height - ...allows the array to be reliably re-assembled after a shutdown - **Assemble**...rebuilds all RAID arrays - `mdadm --assemble --scan`...scan drives for superblocks - partially assembled array...in case of issues - ...automatic during boot...create `mdadm.conf` - ...requires support in initramfs if used for `/` (root-partition) - Scrubbing... - ...regularly read blocks on devices to catch bad blocks early - ...read-error handling...write back of correct data from other devices - ...blocks read successfully...found to not be consistent...**mismatch** ### `/dev/md*` `md` multiple device driver...`man 4 md` - RAID solution that is completely hardware independent... - ...implements the various RAID levels in the kernel disk (block device) code - ...dependent on the server CPU performance and load - `/dev/md*` virtual devices...created from one or more independent underlying devices Basic command syntax... ``` mdadm [mode] <raid-device> [options] <component-devices> ``` ### `mdadm.conf` Configuration file... - ...collection of words separated by white space... `#` for comments - Keywords... - `DEVICE` list devices/partitions t- `ARRAY` identify arrays for assembly - `MAIL{ADDR,FORM}` configure alert mail notification - `CREATE` default for array creation - ...more cf. `man 5 mdadm.conf` ```sh # add a configuration to the end mdadm --detail --scan >> /etc/mdadm.conf ``` `ARRAY` example configuration... ``` ARRAY /dev/md0 metadata=1.2 name=node.fqdn:0 UUID=42650a5c:7eb06556:6db9f264:03ec67e8 ``` - ...second word `/dev/md*` device to assembled...or `ignore` - otherwise...use various heuristics to determine an appropriate name - ...subsequent words identify the array, - `name` identifier...typically the node name with device number as suffix - `uuid` 128 bit...stored in the superblock - `devices`...comma separated list of device names ### Create Create a RAID configuration...mode `--create` - ...writes the per-device superblocks...initialisation... - ...making sure disks of a mirror are identical - or...parity array the parities are correct - `-–level=` RAID level... - `–raid-devices=` number of active devices in the array ```sh # mirror mdadm --create /dev/md0 --level=raid1 --raid-devices=2 /dev/nvme[0-1]n1 # parity raid mdadm --create /dev/md0 --level=raid5 --raid-devices=3 /dev/sd[abc]3 ``` ### Monitor ``` # inspect the configuration in detail mdadm --detail /dev/md0 # detailed information about each RAID device mdadm --examine /dev/sd[bc]1 ``` `/proc/mdstat` snapshot of the kernel's RAID/md state... ```sh watch -n .1 cat /proc/mdstat # ...more details... mdadm --misc --detail /dev/md[012] ``` ### Manage Remove device from array... - `--fail` if not already in failed stated (due to a defect) - `--remove` a device from an array ```sh mdadm /dev/md0 --fail /dev/sda1 --remove /dev/sda1 ``` `--add` new device to array (replacing a failed one probably) ```sh mdadm --add /dev/md0 /dev/sdb1 ``` Stop and delete array... ```sh # unmount the file-systems... umount /dev/md0 # stop the device... mdadm --stop /dev/md0 # remove the device mdadm --remove /dev/md0 # ...incase if it errors with "No such file or directory" mdadm --zero-superblock /dev/sda1 /dev/sdb1 ``` ## `dm-raid` [Device-mapper RAID][01] (dm-raid) target provides a bridge from DM to MD... - ...allows the `mdraid` drivers to be accessed using a device-mapper interface - Supports... - ...RAID device discovery - ...RAID set activation, creation, removal, rebuild - ...display of properties for ATARAID/DDF1 metadata [01]: https://www.kernel.org/doc/html/latest/admin-guide/device-mapper/dm-raid.html ## `lvm` RAID LVM supports RAID... - ...created and managed by LVM using the `mdraid` kernel drivers - ...levels 0, 1, 4, 5, 6, and 10 - Supports snapshots... Create a RAID logical volume using `lvcreate` ```sh lvcreate --type raid1 -m 1 -L 1G -n my_lv my_vg ``` ## ZFS Implements **RAID-Z**... - ...variation on standard RAID-5 that offers better distribution of parity - Eliminates RAID-5 write hole...inconsistency in case of power loss - Three levels... - ...based on the number of parity devices - ...number of disks that can fail while the pool remains operational Pool type in order of performance... - `mirror` – More disks, more reliability, same capacity. (RAID 1) - `raidz1` – Single parity, minimum 3 disks. Two disk failures results in data loss. - `raidz2` – Dual parity, minimum 4 disks. Allows for two disk failures. - `raidz3` – Triple parity, minimum 5 disks. Allows for three disk failures. ```sh zfs list [<name>] # show file-systems zfs set mountpoint=<path> <name> # set target mount point for file-system zfs mount <name> # mount a file-system zfs umount <path> # unmount a file-system grep -i mount= /etc/default/zfs # boot persistance findmnt -t zfs # list mounted file-systems zfs list -o quota <name> # show quota for file-system zfs set quota=<size> <name> # set quota for file-system zpool status [<name>] # show storage pools zpool scrub <name> zpool create <name> <type> <device> [<device>,...] # create a new storage pool ``` ## Btrfs ...ability to combine and manage several disks as one filesystem Supports following RAID profiles... - RAID 1... - RAID 1c3...stores 3 copies on separate disk - RAID 1c4...stores 4 copies on separate disks - RAID 10...RAID1+RAID0 modes for increased performance and redundancy - ...not yet stable or suitable for production use - RAID 5...striped mode with 1 disk as redundancy - RAID 6...striped mode with 2 disks as redundancy ## `storecli` ```sh lspci | grep -i raid # find hardware RAID controllers ``` MegaRAID SAS is the current high-end RAID controllers series by LSI - [StorCLI Reference Manual](https://docs.broadcom.com/doc/12352476) - Search for the [latest version](https://www.broadcom.com/site-search?filters%5Bpages%5D%5Bcontent_type%5D%5Btype%5D=and&filters%5Bpages%5D%5Bcontent_type%5D%5Bvalues%5D%5B%5D=Downloads&page=1&per_page=100&q=storcli) on the Broadcom web-page. - Download will require accepting EULA... - `unzip` the archive - Add the `noarch` to the repository ```sh # list the included packages... >>> find Unified_storcli_all_os -name '*.rpm' Unified_storcli_all_os/ARM/Linux/storcli-007.2007.0000.0000-1.aarch64.rpm Unified_storcli_all_os/Linux/storcli-007.2007.0000.0000-1.noarch.rpm # ...install the command-line tools >>> dnf install -y Unified_storcli_all_os/Linux/storcli-007.2007.0000.0000-1.noarch.rpm # for simplicity... >>> ln -s /opt/MegaRAID/storcli/storcli64 /sbin/storcli ``` `storcli` command interfaces with the RAID controller...following general format... ``` <[object identifier]> <verb> <[adverb | attributes | properties] > <[key=value]> ``` - Object identifiers... - `/cx` controller x - `/cx/vx` virtual drive x on controller x - Verbs... `add`, `del`, `set`, `show`, etc. - `<[adverb | attributes | properties] >`... - ...specifies what the verb modifies or displays - `<[key=value]>` ...if a value is required by the command ```sh # summary of the drive and controller status storcli show # number of controllers detected storcli show ctrlcount # show controller specifics... storcli /c0 show | grep -e ^Product -e ^Serial -e Version # ...controller & virtual devices configuration storcli /c0/v0 show all ``` ### Devices Show the list of devices on a specific controller... - `EID:Slt` enclosure number and slot numbers ```sh # ...first controller in this example >>> storcli /c0 show ... --------------------------------------------------------------------------------- EID:Slt DID State DG Size Intf Med SED PI SeSz Model Sp Type --------------------------------------------------------------------------------- 8:0 9 Onln 0 446.625 GB SATA SSD N N 512B INTEL SSDSC2KG480G8 U - 8:1 10 Onln 0 446.625 GB SATA SSD N N 512B INTEL SSDSC2KG480G8 U - 8:2 16 Onln 1 5.457 TB SAS HDD N N 512B HUS726060AL5210 U - 8:3 11 Onln 1 5.457 TB SAS HDD N N 512B HUS726060AL5210 U - 8:4 12 Onln 1 5.457 TB SAS HDD N N 512B HUS726060AL5210 U - 8:5 13 Onln 1 5.457 TB SAS HDD N N 512B HUS726060AL5210 U - 8:6 14 Onln 1 5.457 TB SAS HDD N N 512B HUS726060AL5210 U - 8:7 15 Onln 1 5.457 TB SAS HDD N N 512B HUS726060AL5210 U - --------------------------------------------------------------------------------- ... ``` ### Configuration Create `add vd` RAID configuration, aka virtual drive... - `r6` aka `type=raid6` - `drives=e:s|e:s-x|e:s-x,y`\ - `e` specifies the enclosure ID, `s` represents the slot - `e:s-x` range convention...slots `s` to `x` in the enclosure `e` - `AWB` (always write back) ignores the non-existence of a cache module - `ra` read ahead should be helpful if the read access is fairly regular - `Strip=64` is believed to by a potentially important parameter... - ...amount of data written to one physical disk before moving to the next one... - ...in reality no one knows about the I/O, so take some middle value here ```sh # created a Raid array storcli /c0 add vd r6 drives=8:2-7 AWB ra cached Strip=64 ``` ### Sanity Checks Basic sanity checks are enable for the RAID controller: * Patrol read checks all disks for bad blocks... - ...if the system load is small - ...should not have a noticeable performance impact * Consistency check for parity...time interval `delay=2016` (roughly 3 month) ```sh # run both consistency checks and patrol reads storcli /c0 set cc=conc delay=2016 starttime=2022/04/28 11 ```