For data backup the data is written onto one or more tape storage systems and read from these when the data is restored.
Tape storage systems are connected to the server via Fibre Channel. These connections may not be used with the storage systems.
The FC channels of the BS2000 servers to the tape storage systems can be almost fully utilized by just a few devices when data backup takes place.
Performance recommendations
Use of ETERNUS CS
Compared to a real tape archive system, ETERNUS CS has the advantage that the data is stored physically on an MTC only when it has been transferred completely to the virtual MTC device. This enables the parallelism of the data backup to be increased without increasing the number of real MTC drives.
LTO tape devices with a direct connection to the server:
Use only preferred quality cartridges
Throughput and compression with directly connected LTO drives
The data written from the server is initially transferred to the LTO device’s cache. Here it is compressed as far as possible by the LTO device. The compressed data is then written to the physical tape in the LTO device. An analogous procedure is used for reading data.
The following performance values apply for LTO devices (without compression of the data in the drive):
Device Type | Maximum Throughput | Capacity |
LTO-4 | 120 Mbyte/s | 800 GB |
LTO-5 | 140 Mbyte/s | 1,500 GB |
LTO-6 | 160 Mbyte/s | 2,500 GB |
These performance values relate to the device / the physical cartridges.
According to information from the LTO vendors, the compression up to LTO-5 is 2:1, and with LTO-6 2 and higher 5:1. With compression in the LTO drive, the following throughput is thus achieved:
LTO-4: up to 240 Mbyte/s
LTO-5: up to 280 Mbyte/s
LTO-6: up to 400 Mbyte/s
LTO-4 drives and higher support “tape encryption” on the hardware side. According to vendor information, when tape encryption is enabled the data rate is reduced by only approx. 1%.
Measurements
The tables below show the possible throughput with an LTO-6 tape device. The load corresponds to data backup using HSMS/ARCHIVE with large tape blocks. The I/Os are performed with a test program from the BS2000 main memory (not from disk) to the MTC device.
The throughput specified is for data which is difficult to compress (compression factor 1) and for data which can be compressed normally (factor 2-3).
The throughput rates specified refer to one task during the actual backup phase, in other words without mounting the tape, without starting and ending the programs, and without creating the report files.
SE700 server, direct connection of an ULTRIUM-TD6 over Fibre Channel (8 Gbit/s)
Compression factor | Throughput | Throughput |
1 | 160 | 160 |
2 - 3 | 356 | 372 |
At 160 Mbyte/s, the maximum throughput of LTO-6 is reached in the case of non-compressible data. When the data is compressed in the tape device, the throughput is near the limit of the maximum throughput of LTO-6.
Measurements on an SE300 server with a comparable tape system yield similar results to when performed on an SE700.