Adaptec RAID1E和 RAID5EE相关知识
1，RAID 1ERAID 1E是RAID 1的增强版本，它并不是我们通常所说的RAID 0+1的组合。RAID 1E的工作原理与RAID1基本上是一样的，只是RAID 1E至少需要3块硬盘才能实现。RAID 1E和RAID 1的工作原理图如下：
可以把RAID1理解成盘与盘之间的镜像，而RAID1E是条带与条带之间的镜像，明显的好处是3块盘也可以做array了，他们都只允许坏一块盘，而RAID1E性能要好点（实际情况还要取决卡的优劣）。
2,RAID 5EE
RAID 5EE是在每个磁盘中预留一部分空间作为分布的热备盘，当一个硬盘出现故障时，这个磁盘上的数据将被压缩到分布的热备盘中，达到数据的保护作用。不过与RAID 5E不同的是RAID 5EE内增加了一些优化技术，使RAID 5EE的工作效率更高，压缩数据的速度也更快。RAID 5EE允许两个磁盘出错，最少需要4个磁盘实现。
RAID 5EE，可以理解成原先的RAID5+SPARE盘模式，只是把SPARE盘的空间条带化并且分布在每块硬盘上，这样一来，SPARE盘也参与读写，性能比RAID5要提高一点，而且在坏了一块盘时恢复也比RAID5快。RAID5有compact和expand模式，expand模式坏掉一块硬盘后，RAID5EE会自动转变为compact模式，在compact模式还可以允许一块盘故障。
RAID 5EE Disk Array
需要注意的是，RAID5EE不能同时坏两块盘；
坏一块盘以后，RAID5EE会自动修复到compact模式，
相当于RAID5；自动修复完成后，才可以再坏一块，
这样一共可以坏两块，但不能同时坏。
如RAID5EE坏了1块盘，自动修复到compact模式以后又坏了一块，
修复方式如下：
先手工添加一块spare盘进行修复到compact模式，
再手工添加一块spare盘继续修复到expand模式。
3,RAID 6
RAID 6是由一些大型企业提出来的私有RAID级别标准，它的全称叫“Independent Data disks with two independent distributed parity schemes（带有两个独立分布式校验方案的独立数据磁盘）”。这种RAID级别是在RAID 5的基础上发展而成，因此它的工作模式与RAID 5有异曲同工之妙，不同的是RAID 5将校验码写入到一个驱动器里面，而RAID 6将校验码写入到两个驱动器里面，这样就增强了磁盘的容错能力，同时RAID 6阵列中允许出现故障的磁盘也就达到了两个，但相应的阵列磁盘数量最少也要4个。
每个磁盘中都具有两个校验值，而RAID 5里面只能为每一个磁盘提供一个校验值，由于校验值的使用可以达到恢复数据的目的，因此多增加一位校验位，数据恢复的能力就越强。不过在增加一位校验位后，就需要一个比较复杂的控制器来进行控制，同时也使磁盘的写能力降低，并且还需要占用一定的磁盘空间。因此，这种RAID级别应用还比较少，相信随着RAID 6技术的不断完善，RAID 6将得到广泛应用。RAID 6的磁盘数量为N+2个。
RAID 6 Disk Array
需要注意的是，Adaptec3805 RAID6可以同时坏两块硬盘，在修复的时候，是一块一块的修复的。RAID6的性能和RAID5EE相当。
4,RAID 60 (Striping and striping with dual party)
Combines multiple RAID 6 sets with RAID 0 (striping). Dual parity allows the failure of two disks in each RAID 6 array. Striping helps to increase capacity and performance without adding disks to each RAID 6 array (which would decrease data availability and could impact performance in degraded mode).
RAID 60 Disk Array
5,RAID Level Comparison
Features
RAID 0
RAID 1
RAID 1E
RAID 5
RAID 5EE
Minimum # Drives
2
2
3
3
4
Data Protection
No Protection
Single-drive failure
Single-drive failure
Single-drive failure
Single-drive failure
Read Performance
High
High
High
High
High
Write Performance
High
Medium
Medium
Low
Low
Read Performance (degraded)
N/A
Medium
High
Low
Low
Write Performance (degraded)
N/A
High
High
Low
Low
Capacity Utilization
100%
50%
50%
67% - 94%
50% - 88%
Typical Applications
High End Workstations, data logging, real-time rendering, very transitory data
Operating System, transaction databases
Operating system, transaction databases
Data warehousing, web serving, archiving
Data warehousing, web serving, archiving
Features
RAID 6
RAID 10
RAID 50
RAID 60
Minimum # Drives
4
4
6
8
Data Protection
Two-drive failure
Up to one disk failure in each sub-array
Up to one disk failure in each sub-array
Up to two disk failure in each sub-array
Read Performance
High
High
High
High
Write Performance
Low
Medium
Medium
Medium
Read Performance (degraded)
Low
High
Medium
Medium
Write Performance (degraded)
Low
High
Medium
Low
Capacity Utilization
50% - 88%
50%
67% - 94%
50% - 88%
Typical Applications
Data archive, backup to disk, high availability solutions, servers with large capacity requirements
Fast databases, application servers
Large databases, file servers, application servers
Data archive, backup to disk, high availability solutions, servers with large capacity requirements
Types of RAID
Types of RAID
Software-Based
Hardware-Based
External Hardware
Description
Best used for large block applications such as data warehousing or video streaming. Also where servers have the available CPU cycles to manage the I/O intensive operations certain RAID levels require.
Included in the OS, such as Windows®, Netware, and Linux. All RAID functions are handled by the host CPU which can severely tax its ability to perform other computations.
Best used for small block applications such as transaction oriented databases and web servers.
Processor-intensive RAID operations are off-loaded from the host CPU to enhance performance.
Battery-back write back cache can dramatically increase performance without adding risk of data loss.
Connects to the server via a standard controller. RAID functions are performed on a microprocessor located on the external RAID controller independent of the host.
Advantages
Low price
Only requires a standard controller
Data protection and performance benefits of RAID
More robust fault-tolerant features and increased performance versus software-based RAID
OS independent
Build high-capacity storage systems for highend servers
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