RAID 0+1 (striped mirrors) The combination of striping and mirroring provides the performance benefits of RAID 0 and the redundancy benefits of RAID 1. This option is also known as RAID 1+0 and RAID 10. RAID 5 (rotated parity) RAID 5 presents a logical disk composed of multiple physical disks with data striped across the disks in sequential blocks (stripe units). However, the underlying physical disks have parity information scattered throughout the disk array, as Figure 3 shows. For read requests, RAID 5 has characteristics that are similar to those of RAID 0. However, small RAID 5 writes are much slower than those of JBOD or RAID 0 because each parity block that corresponds to the modified data block requires three additional disk requests. Because four physical disk requests are generated for every logical write, bandwidth is reduced by approximately 75%. RAID 5 provides data recovery capabilities because data can be reconstructed from the parity. RAID 5 can survive the loss of any one physical disk, as opposed to RAID 1, which can survive the loss of multiple disks as long as an entire mirrored set isn’t lost. RAID 5 requires additional time to recover from a lost physical disk compared to RAID 1 because the data and parity from the failed disk can be recreated only by reading all the other disks. Performance during the rebuilding period is severely reduced due only due to the rebuilding traffic but also because the reads and writes that target the data that was stored on the failed disk must read all disks (an entire "stripe") to re-create the missing data. RAID 5 is less expensive than RAID 1 in that it requires only the addition of a single disk per array, rather than double the total amount of disks in an array. RAID 6 redundancy) RAID 6 is basically RAID 5 with additional redundancy built in. Instead of a single block of parity per stripe of data, two blocks of redundancy are included. The second block uses a different redundancy code (as opposed to parity), which allows data to be reconstructed after the loss of any two disks. Alternatively, disks can be arranged in a two-dimensional matrix, and both vertical and horizontal parity can be maintained. Rotated redundancy schemes (such as RAID 5 and 6) are the most difficult to understand and plan for. Figure 3 illustrates RAID 5. Figure 3. RAID 5 Overview Choosing the RAID Level Each RAID level involves a trade-off between the following factors: Cost Performance Availability Reliability
You can determine the best RAID level for your servers by evaluating the read and write loads of the various data types and then deciding how much you are willing to spend to achieve the performance and availability/reliability that your organization requires. Table 8 describes common RAID levels and their relative costs, performance, availability, and reliability. Table 8. RAID Trade-Offs Performance Reliability Availability Cost and capacity JBOD Pros: Concurrent sequential streams to separate disks. Cons: Susceptibility to load imbalance. Pros: Data isolation; single loss affects one disk. Cons: Data loss after one failure. Pros: Single loss does not prevent access to other disks. Pros: Minimum cost. RAID 0 (striping) Pros: Balanced load. Potential for better response times, throughput, and concurrency. Cons: Difficult stripe unit size choice. Cons: Data loss one failure. Single loss affects entire array. Cons: Single loss prevents access to entire Pros: Minimum cost. Two-disk minimum. RAID 1 (mirroring) Pros: Two data sources for every read request (up to 100% performance boost). Cons: Writes must update all mirrors. Pros: Single loss and often multiple losses (in large configurations) are survivable. Pros: Single loss and often multiple losses (in large configurations) do not prevent access. Pros: Twice the cost of RAID 0 or JBOD. Two-disk minimum. RAID 0+1 (striped mirrors) Pros: Two data sources for every read request (up to 100% performance boost). Balanced load. Potential for better response times, throughput, and concurrency. Cons: Writes must update mirrors. Difficult stripe unit size choice. Pros: Single loss and often multiple losses (in large configurations) are survivable. Pros: Single loss and often multiple losses (in large configurations) do not prevent access. Pros: Twice the cost of RAID 0 or JBOD. Four-disk minimum.
RAID 5 (rotated parity) Pros: Balanced load. Potential for better read response times, throughput, and concurrency. Cons: Up to 75% write performance hit due to RMW. Read performance degrades in failure mode. All sectors that must be read for reconstruction; major slowdown. Danger of data in invalid state after power loss and recovery. Pros: Single loss survivable; requests might still corrupt. Cons: Multiple losses affect entire array. After a single loss, array is vulnerable until reconstructed. Pros: Single loss does not prevent access. Cons: Multiple losses prevent access to entire array. To speed reconstruction, application access might be slowed or stopped. Pros: One additional disk required. Three-disk minimum. RAID 6 (two separate erasure codes) Pros: Balanced load. Potential for better read response times, throughput, and concurrency. Cons: Up to 83% performance hit due to multiple RMW. Read performance degrades in failure mode. All sectors must be read for reconstruction: major slowdown. Danger of data in invalid state after power loss and recovery. Pros: Single loss survivable; "inflight" write requests might still corrupt. Cons: >2 losses affect entire 2 losses, array is vulnerable until reconstructed. Pros: Single loss does not prevent access. Cons: >2 losses prevent access to entire array. To speed reconstruction, application access might be slowed or stopped. Pros: Two additional disks required. Five-disk minimum. The following are sample uses for various RAID levels: JBOD: Concurrent video streaming. RAID 0: Temporary or reconstructable data, workloads that tend to develop hot spots in the data, and workloads with high degrees of unrelated concurrency. RAID 1: Database logs, and critical data and concurrent sequential streams. RAID 0+1: A general-purpose combination of performance and reliability for critical data, workloads with hot spots, and high-concurrency workloads. RAID 5: Web semicritical data, workloads without small writes, scenarios where capital and operating costs are an overriding factor, and read-dominated workloads.
Minimize the impact on CPU usage when running a large number of Terminal Server sessions by opening the MMC snap-in for Group Policies (gpedit.msc) and making the following changes under Local Computer Policy > User Configuration > Administrative Templates: Under Start Menu and Taskbar, enable Do not keep history of recently opened documents. Start Menu and Taskbar, enable Remove Balloon Tips on Start Menu items. Under Start Menu and Taskbar, enable Remove frequent program list from Start Menu. Minimize the impact on the memory footprint and reduce background activity by disabling certain Microsoft Win32® services. The following are snippets from command-line scripts to accomplish this: Service name Syntax to stop and disable service Desktop Window Manager Session Manager sc config UxSms start= disabled sc stop UxSms Windows Error Reporting service sc config WerSvc start= disabled sc stop WerSvc Windows Update sc config wuauserv start= disabled sc stop wuauserv Minimize background traffic by applying the following changes under Start > All Programs > Administrative Tools > Server Manager, and going to Resources and Support: Opt out of participating in the Customer Experience Improvement Program (CEIP). Opt out of participating in Windows Error Reporting (WER). Apply the following changes from the Terminal Services MMC snap-in (tsconfig.msc): Set the maximum color depth to 24 bits per pixel (bpp). Disable all device redirections. Navigate to Start > All Programs > Administrative Tools > Terminal Services > Terminal Services Configuration and change the Client Settings from the RDP-Tcp properties as follows: Limit the Maximum Color Depth to 24 bpps. Disable redirection for all available devices such as Drive, Windows Printer, LPT Port, COM Port, Clipboard, Audio, Supported Plug and Play Devices, and Default to main client printer. Monitoring and Data Collection The following list of performance counters is considered a base set of counters when monitoring the resource usage on the Terminal Server workload. Log the performance counters to a local, raw (blg) performance counter log. It is less expensive to collect all instances (‘*’ wide character) and then extract particular instances while post-processing by using relog.exe. \Cache\* \IPv4\* \LogicalDisk(*)\* \Memory\* \Network Interface(*)\*