raid

 

 

 


Dell H710

 

Default: SAS

The H710 is backwards compatible with SATA

You can't mix SAS and SATA within a virtual disk.

Software: megacli

https://datahunter.org/megacli

 


Adaptec

 

HomePage: http://storage.microsemi.com/en-us/support/raid/

lspci | grep RAID

01:01.0 RAID bus controller: Adaptec AAC-RAID (rev 01)

lspci | less

01:01.0 RAID bus controller: Adaptec AAC-RAID (rev 01)
        Subsystem: Adaptec AAR-2810SA PCI SATA 8ch (Corsair-8)
        Flags: bus master, 66MHz, slow devsel, latency 32, IRQ 22
        Memory at f0000000 (32-bit, prefetchable) [size=64M]
        Expansion ROM at ff910000 [disabled] [size=32K]
        Capabilities: [80] Power Management version 2
        Kernel driver in use: aacraid
        Kernel modules: aacraid

Hardware info: http://storage.microsemi.com/en-us/support/raid/sata/aar-2810sa/

Adaptec Storage Manager for Linux.

 


ASM (Adaptec Storage Manager)

 

arcconf getconfig 1

Controllers found: 1

----------------------------------------------------------------------
Controller information
----------------------------------------------------------------------
   Controller Status                   : Optimal
   Channel description                 : SATA
   Controller Model                    : Adaptec 2810SA
   Controller Serial Number            : C695E4
   Physical Slot                       : 2
   Installed memory                    : 64 MB
   Copyback                            : Disabled
   Background consistency check        : Disabled
   Defunct disk drive count            : 0
   Logical devices/Failed/Degraded     : 1/0/0
   ---------------------------------------------------
   Controller Version Information
   ---------------------------------------------------
   BIOS                                : 4.2-0 (7348)
   Firmware                            : 4.2-0 (7348)
   Driver                              : 1.2-0 (29801)
   Boot Flash                          : 0.0-0 (0)
   ---------------------------------------------------
   Controller Battery Information
   ---------------------------------------------------
   Status                              : Not Installed

# Adapter information

arcconf GETCONFIG 1 AD

# Logical device information

arcconf GETCONFIG 1 LD

# Physical device information

arcconf GETCONFIG 1 PD

 


HBA & RAID mode

 

HBA just means 'Host Bus Adapter'

JBOD VS HBA mode ?

 


RAID 1

 

Disks already have error detection built in (RAID1 是依賴 HDD 自身的 error detection)

A typical RAID 1 implementation will pick one disk to read from, (沒有每次讀兩碟 Compare)

reading from the other disk only if the first disk reports an error.

 

Typically, the RAID array can be scanned periodically(Patrol Read)

During this operation, both disks are compared.

The primary purpose is to detect any bad sectors and rewrite them with data from the other disk
 


RAID5

 

With RAID5, the parity information is not used until the failure of a drive is detected

RAID5 的核心 -  XOR 運算

# HDD0     HDD1    HDD2        HDD(n-1)       HDDn
   D0  xor  D1 xor  D2  xor ... D(n-1)     =   P0

D0, D1, D2= Data

P0 = parity

Data 的 mismatch 問題

RAID1 or RAID5 would not protect against "mismatch"(bit that randomly "flipped")

They are mainly meant to protect against the hardware failure of a single drive

解決

A) Using RAID6

B) Use a file system which actively checks for data integrity, such as ZFS, btrfs.

* HDD in-built redundancy for error correction and recovery

Modern drives make extensive use of error correction codes (ECCs), particularly Reed–Solomon error correction.

In the newest drives, as of 2009, low-density parity-check codes (LDPC) were supplanting Reed–Solomon;

(LDPC codes enable performance close to the Shannon Limit and thus provide the highest storage density available)

The worst type of errors are silent data corruptions which are errors undetected by the disk firmware or the host operating system;

S.M.A.R.T: "Hardware ECC Recovered"

C3  ECC Error Rate
C7  CRC Error Count
C8  Write Error Rate / Multi Zone Error Rate

The higher the raw value, the worse the disk surface condition and/or mechanical subsystem is.

 


RAID10 Mode

 

When configuring a RAID10 array it is necessary to specify

- the number of replicas of each data block that are required (this will normally be 2)

- replicas should be 'near', 'offset' or 'far' (mdadm layout option)

The default is 'n2'

n2

each chunk is repeated n times in a k-way stripe array

(k is the number of drives)

2 drives         3 drives            4 drives
--------         ----------        --------------
A1  A1           A1  A1  A2        A1  A1  A2  A2
A2  A2           A2  A3  A3        A3  A3  A4  A4
A3  A3           A4  A4  A5        A5  A5  A6  A6
A4  A4           A5  A6  A6        A7  A7  A8  A8
..  ..           ..  ..  ..        ..  ..  ..  ..

f2

All the drives are divided into f sections.

All the chunks are repeated in each section but offset by one device.

2 drives             3 drives
--------             --------------
A1  A2               A1   A2   A3
A3  A4               A4   A5   A6
A5  A6               A7   A8   A9
..  ..               ..   ..   ..
A2  A1               A3   A1   A2
A4  A3               A6   A4   A5
A6  A5               A9   A7   A8

o2

each stripe is repeated o times

2 drives       3 drives
--------       --------
A1  A2         A1  A2  A3
A2  A1         A3  A1  A2
A3  A4         A4  A5  A6
A4  A3         A6  A4  A5
A5  A6         A7  A8  A9
A6  A5         A9  A7  A8
..  ..         ..  ..  ..

 


RAID6

 

dual parity calculation works

P = a + b
Q = a + 2b

If you lost c and d, you can recover them by solving the original equations.

the calculated values of P and Q can be significantly larger than the original data values.

We 'd like to redefine the arithmetic operators +, –, ×, / such that our equations still work,

but the values of P and Q stay within the ranges of the input values.

The solution is called a Galois field. The particular Galois field of interest is GF(28)

it gives us efficient +, –, ×, / operators that we can use to calculate P and Q,

and if needed recalculate a lost data block from the remaining data blocks and parities.

And, each of P and Q perfectly fits into a byte. The resulting coding is called Reed-Solomon error correction,

and that 's the method used by RAID 6 configuration

 


Dell H710 - RAID 10

 

RAID 10 = Nested RAID

Creates a striped set from a series of mirrored drives

RAID 10 = RAID 0 ( RAID 1 + RAID 1)

 * each RAID 1 set is considered a span

Updated algorithm RAID 1

Updated algorithm enables each RAID-1 array to contain 2–32 drives

Drive count must be even

Each drive has a mirrored pair

Span 與 Stripe

Span: 幾個物理磁片一個接一個串聯到一起, 從而提供一個大的邏輯磁片 (JBOD)

(Concatenation or spanning)

It is not one of the numbered RAID levels

RAID 0 = stripe set