Sizing Guide Exchange Server 2003 - Fujitsu

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White Paper Sizing Guide Exchange Server 2003 Version: 4.2, July 2006 RAID 1+0 Also occasionally referred to as RAID 10. Actually it is not a separate RAID level, but merely RAID 0 combined with RAID 1. Thus the features of the two basic levels - security and sequential performance - are combined. RAID 1+0 uses an even number of hard disks. Two disks are combined and the data are mirrored (RAID 1). The data are distributed over this pair of disks (RAID 0). RAID 1+0 is particularly suited for the redundant storing of large files. Since no parity has to be calculated in this case, write access with RAID 1+0 is very fast. RAID 0+1 In addition to the RAID level combination 1+0 there is also the combination 0+1. For half the hard disks a RAID 0 array is formed and the information is then mirrored onto the other half (RAID 1). As regards performance RAID 0+1 and 1+0 are identical. However, RAID 1+0 has a higher degree of availability than RAID 0+1. If a disk fails with RAID 0+1, redundancy is no longer given. With a RAID 1+0, however, further disks may fail as long as the same RAID 1 pair is not affected. The likelihood of both disks of a RAID 1 pair failing in a RAID 1+0 consisting RAID 1+0 RAID 0 of n disks 2 /(n²-n) is considerably less than the probability of two disks that do not belong to a pair being affected (2n-4) /(n²-n). Others There are a number of other RAID levels that are in part no longer in use today, or other combinations, such as RAID 5+0. More information about the different RAID levels is to be found in the white paper Performance Report – Modular RAID [L5]. For all RAID levels care must be taken that hard disks of the same capacity and same performance are used. Otherwise, the smallest hard disk determines the overall capacity or the slowest hard disk the overall performance. The performance of the RAID array is on the one hand determined by the RAID level used, but also by the number of disks in an array. Even the RAID controllers themselves show differing performances particularly for more complex RAID algorithms such as RAID 5. Even parameters such as block and stripe size, which have to be defined when setting up the RAID array also ultimately influence the efficiency of a RAID array. The diagram opposite shows the relative performance of various RAID arrays. © Fujitsu Technology Solutions, 2009 Page 22 (69) A E A’ E’ RAID 0+1 A E A’ E’ B F B’ F’ B F B’ F’ RAID 0 C G C’ G’ C G C’ G’ D H D’ H’ D H D’ H’ RAID 1 RAID 1
White Paper Sizing Guide Exchange Server 2003 Version: 4.2, July 2006 Data throughput Current SCSI RAID controllers provide a data throughput of 320 MB/s per SCSI channel. This is more than adequate for database-oriented applications, even if 7 or more hard disks are operated on one channel. Frequently with regard to the number of disks on an SCSI channel the maximum data transfer rate of the SCSI bus is mistakenly divided by the peak data transfer rate of the hard disk. With fast hard disks this may very well be over 80 MB/s, according to which an SCSI bus would then already be at full capacity with four hard disks. However, this calculation is incorrect as it only applies to a theoretical extreme situation. The diagram below shows the real situation. It can be seen that the theoretical curve is roughly achieved only with purely sequential read with large data blocks, as is the case with video streaming. If write operations are added, the data throughput slumps decidedly. For random access with block sizes of 4 and 8 kB, as is the case with access to the Exchange database, the throughput is only just approximately 10 MB/s. This means that the maximum possible number of hard disks can be run on one SCSI bus without any trouble. SCSI RAID controllers provide up to 4 SCSI buses. Consequently the possible throughput adds up in principle. Therefore it is important for such controllers to also be used in an adequate PCI slot. The table opposite shows the various PCI bus speeds and the throughputs ascertained with them. However, the data throughputs also depend on the type and number of the controllers used as well as on the memory interface (chip set) of the server. In order to harmonize the controller type and ensure its number with the server, each of these is tested and certified for the individual systems by Fujitsu. In this connection, the system configurator determines which and how many controllers can be sensibly used per system. PCI Bus Throughput in MB/s theoretical measured PCI 33 MHz, 32-bit 133 82 PCI 33 MHz, 64-bit 266 184 PCI-X 66 MHz, 64-bit 533 330 PCI-X 100 MHz, 64-bit 800 n/a PCI-X 133 MHz, 64-bit 1066 n/a PCI-E 2500 MHz, 1× 313 250 PCI-E 2500 MHz, 2× 625 500 PCI-E 2500 MHz, 4× 1250 1000 PCI-E 2500 MHz, 8× 2500 2000 PCI-E 2500 MHz, 16× 5000 4000 © Fujitsu Technology Solutions, 2009 Page 23 (69)
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Sizing Guide Exchange Server 2003 - Fujitsu

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