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November 2013 |
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Online Capacity Expansion is officially supported for RAID levels 0, 5, 6, and 10 by adding additional disks.
- Although not officially supported, see the following slide for what is technically possible for Adaptec 5, 6, 7, and 8 series RAID controllers. Internal tests were conducted in lab environments; not recommended for live production environments.
- It is also technically possible to increase the size of a RAID 1 or 10 array by replacing existing drives with larger capacity drives, one by one, until all disks have unused, free space. Simply right-click a logical device (array) and choose 'Expand or change logical device'.
Please ensure you have a FULL BACKUP before attempting OCE or RLM.
See related article:
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October 2013 |
A PC has a spine and this spine is evolving with time. This training note explains what the PC spine is, how it has evolved, and its impact on computer uses.
 The history of PC is quite short and is less than 50 years. Think of the PC as human without limbs. PC has a head and a spine. CPU is the head which can think and memorize. What is the spine? The spine provides the main skeleton of the body and accommodates the nerve to connect various parts of the body with the brain. In the early years, the spine had a few segments and they were called the North Bridge (GMCH), South Bridge (ICH), and BIOS (FWH). See the illustration. Each segment had its own path for communicating. This design is clumsy.
Whilst we would expect the development to be towards a single segment spine, PC has gone a different direction and we are seeing multiple single segment spines! This direction is to allow the PC to have more limbs than human in order to serve human better. The good news is that all spines are based on one single design called PCIe for Peripheral Control Interconnect Express which makes a lot of sense. Note that the PCIe has emerged from a minor role to a major role.
We are currently on PCIe 3.0 with a data transfer capability of 8Gbps per link and an aggregation capacity of 16 links per bridge. This means the aggregated data transfer is as high as 128Gbps between 2 points inside the PC. Assume 8 bits form 1Byte. We have 16GB/s. This is higher than the memory talking to the CPU (being 11GB/s for DDR3). This is impressive- the spine is faster than the memory. Note: Some systems have multiple DDR3 controllers and the remark would not be valid.
Both the memory and the spine will evolve to the 4th generation: DDR4 and PCIe 4.0. DDR4 will have a single link transfer rate of 24GB/s and PCIe 4.0 an aggregated rate of 32GB/s.
Owing to this trend, it has become practical for a PC to have more limbs to reach out to the outer world. Devices for reaching out consist of USB, LAN, and Thunderbolt. USB is going to version 3.1 soon with a data transfer rate of 10Gb/s whereas Ethernet LAN is going to hit 40Gb/s. Thunderbolt will reach 20Gb/s and is mainly a threat to USB for reaching out to peripherals. Ethernet will stay for inter-computer connections, and it competes with another standard called Infiniband for domination.
Thunderbolt is designed like PCIe and is therefore a natural candidate for future peripheral connection. Similarly, a new idea has surfaced and it is called Switching over PCIe. A PCIe Switch is able to connect 2 PC for example via a PCIe card in each PC. The data transfer rate is 128Gb/s (see above underlined) which is readily higher than Ethernet 40Gb/s. This is a recent development and we are seeing some signs of technology unification which will provide a good basis for simplifying further developments.
END
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October 2013 |
A PC has a spine and this spine is evolving with time. This training note explains what the PC spine is, how it has evolved, and its impact on computer uses.
The history of PC is quite short and is less than 50 years. Think of the PC as human without limbs. PC has a head and a spine. CPU is the head which can think and memorize. What is the spine? The spine provides the main skeleton of the body and accommodates the nerve to connect various parts of the body with the brain. In the early years, the spine had a few segments and they were called the North Bridge (GMCH), South Bridge (ICH), and BIOS (FWH). See the illustration. Each segment had its own path for communicating. This design is clumsy.
Whilst we would expect the development to be towards a single segment spine, PC has gone a different direction and we are seeing multiple single segment spines! This direction is to allow the PC to have more limbs than human in order to serve human better. The good news is that all spines are based on one single design called PCIe for Peripheral Control Interconnect Express which makes a lot of sense. Note that the PCIe has emerged from a minor role to a major role.
We are currently on PCIe 3.0 with a data transfer capability of 8Gbps per link and an aggregation capacity of 16 links per bridge. This means the aggregated data transfer is as high as 128Gbps between 2 points inside the PC. Assume 8 bits form 1Byte. We have 16GB/s. This is higher than the memory talking to the CPU (being 11GB/s for DDR3). This is impressive- the spine is faster than the memory. Note: Some systems have multiple DDR3 controllers and the remark would not be valid.
Both the memory and the spine will evolve to the 4th generation: DDR4 and PCIe 4.0. DDR4 will have a single link transfer rate of 24GB/s and PCIe 4.0 an aggregated rate of 32GB/s.
Owing to this trend, it has become practical for a PC to have more limbs to reach out to the outer world. Devices for reaching out consist of USB, LAN, and Thunderbolt. USB is going to version 3.1 soon with a data transfer rate of 10Gb/s whereas Ethernet LAN is going to hit 40Gb/s. Thunderbolt will reach 20Gb/s and is mainly a threat to USB for reaching out to peripherals. Ethernet will stay for inter-computer connections, and it competes with another standard called Infiniband for domination.
Thunderbolt is designed like PCIe and is therefore a natural candidate for future peripheral connection. Similarly, a new idea has surfaced and it is called Switching over PCIe. A PCIe Switch is able to connect 2 PC for example via a PCIe card in each PC. The data transfer rate is 128Gb/s (see above underlined) which is readily higher than Ethernet 40Gb/s. This is a recent development and we are seeing some signs of technology unification which will provide a good basis for simplifying further developments.
END
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October 2013 |
We have been on DDR3 for several years as of 2013. During these years, we have seen a range of memory from DDR3-800 to DDR3-2000. What do these numbers mean? What can we expect in the future from memory technology? What do we really want from memory?
- Human has short term memory and long term memory. Computers are similar. Short term memory is the main memory. Long term memory is the hard disk. This training note focuses on computer main memory. Surprising, it is not just short term and it is volatile. The memory will disappear if the computer power is turned off. This type of memory is called Dynamic Random Access Memory (DRAM). DDR3 is DRAM.
- Fortunately USB memory sticks are not volatile so that we can keep data or video files on USB for several years perhaps. USB memory sticks use the same type of technology as SSD (static state disk) called NAND (Not AND). NAND is non-volatile but it allows ‘data written to it” for a finite number of times and the speed of writing and reading is much lower than DRAM.
- DDR3 stands for Double Data Rate Generation 3 and it succeeded DDR2, DDR, and SDR (Single) in reversed chronological order. All of them are DRAM. SDR used 1 clock signal to initiate one memory transfer. DDR used 1 clock signal for 2 transfers. DDR2 gets 4 transfers and DDR3 gets 8 transfers. DDR3-800 is therefore based on a 100MHz clock. These numbers are deceiving as the multipliers do not deliver correspondingly.
- Users care about the effective rate of data transfer and not the physical clock frequency or multipliers. One literature stated DDR3 as having 11GB/s. If a motherboard and its CPU are designed with 3 memory controllers, we can expect the data rate to increase to 33GB/s. Intel Core i7 with 2011pin is designed to have 4 memory controllers and it can hit 44GB/s in theory.
 The specifications for DDR4 have been completed by an international standard organisation called JEDEC. Preliminary tests claimed a data transfer rate of 24GB/s which is more than double of DDR3. This increase is not achieved with higher clock frequency along the DDR2 or DDR3 approaches, but is from a complete re-design. DDR2 and DDR3 use a parallel signal transmission scheme which requires the beginnings and ends of all signal transmission paths to be synchronized. DDR4 uses a packet signal transmission scheme which does not need to wait to get synchronized. DDR4 is not backward compatible with DDR3, and it will be available in computer systems on the market in year 2015.
Memory speed is important for the performance of computers.
END
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October 2013 |
We have been on DDR3 for several years as of 2013. During these years, we have seen a range of memory from DDR3-800 to DDR3-2000. What do these numbers mean? What can we expect in the future from memory technology? What do we really want from memory?
- Human has short term memory and long term memory. Computers are similar. Short term memory is the main memory. Long term memory is the hard disk. This training note focuses on computer main memory. Surprising, it is not just short term and it is volatile. The memory will disappear if the computer power is turned off. This type of memory is called Dynamic Random Access Memory (DRAM). DDR3 is DRAM.
- Fortunately USB memory sticks are not volatile so that we can keep data or video files on USB for several years perhaps. USB memory sticks use the same type of technology as SSD (static state disk) called NAND (Not AND). NAND is non-volatile but it allows ‘data written to it” for a finite number of times and the speed of writing and reading is much lower than DRAM.
- DDR3 stands for Double Data Rate Generation 3 and it succeeded DDR2, DDR, and SDR (Single) in reversed chronological order. All of them are DRAM. SDR used 1 clock signal to initiate one memory transfer. DDR used 1 clock signal for 2 transfers. DDR2 gets 4 transfers and DDR3 gets 8 transfers. DDR3-800 is therefore based on a 100MHz clock. These numbers are deceiving as the multipliers do not deliver correspondingly.
- Users care about the effective rate of data transfer and not the physical clock frequency or multipliers. One literature stated DDR3 as having 11GB/s. If a motherboard and its CPU are designed with 3 memory controllers, we can expect the data rate to increase to 33GB/s. Intel Core i7 with 2011pin is designed to have 4 memory controllers and it can hit 44GB/s in theory.
- The specifications for DDR4 have been completed by an international standard organisation called JEDEC. Preliminary tests claimed a data transfer rate of 24GB/s which is more than double of DDR3. This increase is not achieved with higher clock frequency along the DDR2 or DDR3 approaches, but is from a complete re-design. DDR2 and DDR3 use a parallel signal transmission scheme which requires the beginnings and ends of all signal transmission paths to be synchronized. DDR4 uses a packet signal transmission scheme which does not need to wait to get synchronized. DDR4 is not backward compatible with DDR3, and it will be available in computer systems on the market in year 2015.
Memory speed is important for the performance of computers.
END
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