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What is a "Softraid controller"?
I thought software raid was simply using windows to mirror two drives, on standard disk controllers. So what is this card I have called a Silicon Image Softraid controller? It does hardware raid (as I would name it) - I can set up arrays in it's own bios before an OS loads. So why do they call it softraid? Is that just referring to the ability to manage the volumes within the OS?
-- Attila the Hun died during a bout of rough sex where his partner broke his nose causing a haemorrhage. |
#2
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What is a "Softraid controller"?
Jimmy Wilkinson Knife wrote:
I thought software raid was simply using windows to mirror two drives, on standard disk controllers. So what is this card I have called a Silicon Image Softraid controller? It does hardware raid (as I would name it) - I can set up arrays in it's own bios before an OS loads. So why do they call it softraid? Is that just referring to the ability to manage the volumes within the OS? Whether it's a SIL3112 or an Intel RST, these things are just SATA ports, where any notion of RAID is provided by a driver hiding the details from you. A real RAID card has an IOP and/or "XOR chip" to support RAID5 without burdening the CPU for XOR processing. A real RAID card may also have a small DIMM onboard for caching (to smooth writing to the array, depending on RAID type). Paul |
#3
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What is a "Softraid controller"?
On Fri, 25 May 2018 18:22:49 +0100, Paul wrote:
Jimmy Wilkinson Knife wrote: I thought software raid was simply using windows to mirror two drives, on standard disk controllers. So what is this card I have called a Silicon Image Softraid controller? It does hardware raid (as I would name it) - I can set up arrays in it's own bios before an OS loads. So why do they call it softraid? Is that just referring to the ability to manage the volumes within the OS? Whether it's a SIL3112 or an Intel RST, these things are just SATA ports, where any notion of RAID is provided by a driver hiding the details from you. A real RAID card has an IOP and/or "XOR chip" to support RAID5 without burdening the CPU for XOR processing. A real RAID card may also have a small DIMM onboard for caching (to smooth writing to the array, depending on RAID type). But this card (a Sil 3132) can create a mirror in hardware. I switched the machine on and went into the RAID card's BIOS, before the OS had loaded at all. I told it to copy one normal system disk containing Windows 10 onto a second one, to create a mirror. It did this without booting the OS. For some reason this card is sold as a "Softraid controller". -- Peter is listening to "DJ Splash - Ring dinge ding" |
#4
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What is a "Softraid controller"?
Jimmy Wilkinson Knife wrote:
On Fri, 25 May 2018 18:22:49 +0100, Paul wrote: Jimmy Wilkinson Knife wrote: I thought software raid was simply using windows to mirror two drives, on standard disk controllers. So what is this card I have called a Silicon Image Softraid controller? It does hardware raid (as I would name it) - I can set up arrays in it's own bios before an OS loads. So why do they call it softraid? Is that just referring to the ability to manage the volumes within the OS? Whether it's a SIL3112 or an Intel RST, these things are just SATA ports, where any notion of RAID is provided by a driver hiding the details from you. A real RAID card has an IOP and/or "XOR chip" to support RAID5 without burdening the CPU for XOR processing. A real RAID card may also have a small DIMM onboard for caching (to smooth writing to the array, depending on RAID type). But this card (a Sil 3132) can create a mirror in hardware. I switched the machine on and went into the RAID card's BIOS, before the OS had loaded at all. I told it to copy one normal system disk containing Windows 10 onto a second one, to create a mirror. It did this without booting the OS. For some reason this card is sold as a "Softraid controller". The card has a ROM. The ROM code includes INT 0x13 support. The ROM code is loaded by the BIOS, into a 256KB area reserved for such codes. You can include in that code, a standalone BIOS page for "doing stuff" to the disks on the controller. For example, pressing ctrl-I might bring up that page. You can define an array there, or rebuild an array there... although a runtime rebuild in the background is the preferred method (less downtime). When you have enough storage controller cards populated in a machine, there might not be enough memory space to load the ROM. This results in a failure in the ability to boot, for the card which is "furthest" from the CPU socket. The BIOS loads those ROM images, and unnecessary parts of them "shrink", all in the name of making as much of the 256KB available as possible. For example, the video card can have a 64KB ROM on it. If you had several video cards, there might not be room to load anything else. Paul |
#5
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What is a "Softraid controller"?
On Fri, 25 May 2018 23:02:30 +0100, Paul wrote:
Jimmy Wilkinson Knife wrote: On Fri, 25 May 2018 18:22:49 +0100, Paul wrote: Jimmy Wilkinson Knife wrote: I thought software raid was simply using windows to mirror two drives, on standard disk controllers. So what is this card I have called a Silicon Image Softraid controller? It does hardware raid (as I would name it) - I can set up arrays in it's own bios before an OS loads. So why do they call it softraid? Is that just referring to the ability to manage the volumes within the OS? Whether it's a SIL3112 or an Intel RST, these things are just SATA ports, where any notion of RAID is provided by a driver hiding the details from you. A real RAID card has an IOP and/or "XOR chip" to support RAID5 without burdening the CPU for XOR processing. A real RAID card may also have a small DIMM onboard for caching (to smooth writing to the array, depending on RAID type). But this card (a Sil 3132) can create a mirror in hardware. I switched the machine on and went into the RAID card's BIOS, before the OS had loaded at all. I told it to copy one normal system disk containing Windows 10 onto a second one, to create a mirror. It did this without booting the OS. For some reason this card is sold as a "Softraid controller". The card has a ROM. The ROM code includes INT 0x13 support. The ROM code is loaded by the BIOS, into a 256KB area reserved for such codes. You can include in that code, a standalone BIOS page for "doing stuff" to the disks on the controller. For example, pressing ctrl-I might bring up that page. You can define an array there, or rebuild an array there... although a runtime rebuild in the background is the preferred method (less downtime). When you have enough storage controller cards populated in a machine, there might not be enough memory space to load the ROM. This results in a failure in the ability to boot, for the card which is "furthest" from the CPU socket. The BIOS loads those ROM images, and unnecessary parts of them "shrink", all in the name of making as much of the 256KB available as possible. For example, the video card can have a 64KB ROM on it. If you had several video cards, there might not be room to load anything else. So once I've entered Windows, the ROM is disabled and it's software controlled by the driver? Is there such a think as a RAID controller which doesn't do that? -- The true mark of a civilized society is when its citizens know how to hate each other peacefully. |
#6
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What is a "Softraid controller"?
Jimmy Wilkinson Knife wrote:
On Fri, 25 May 2018 23:02:30 +0100, Paul wrote: Jimmy Wilkinson Knife wrote: On Fri, 25 May 2018 18:22:49 +0100, Paul wrote: Jimmy Wilkinson Knife wrote: I thought software raid was simply using windows to mirror two drives, on standard disk controllers. So what is this card I have called a Silicon Image Softraid controller? It does hardware raid (as I would name it) - I can set up arrays in it's own bios before an OS loads. So why do they call it softraid? Is that just referring to the ability to manage the volumes within the OS? Whether it's a SIL3112 or an Intel RST, these things are just SATA ports, where any notion of RAID is provided by a driver hiding the details from you. A real RAID card has an IOP and/or "XOR chip" to support RAID5 without burdening the CPU for XOR processing. A real RAID card may also have a small DIMM onboard for caching (to smooth writing to the array, depending on RAID type). But this card (a Sil 3132) can create a mirror in hardware. I switched the machine on and went into the RAID card's BIOS, before the OS had loaded at all. I told it to copy one normal system disk containing Windows 10 onto a second one, to create a mirror. It did this without booting the OS. For some reason this card is sold as a "Softraid controller". The card has a ROM. The ROM code includes INT 0x13 support. The ROM code is loaded by the BIOS, into a 256KB area reserved for such codes. You can include in that code, a standalone BIOS page for "doing stuff" to the disks on the controller. For example, pressing ctrl-I might bring up that page. You can define an array there, or rebuild an array there... although a runtime rebuild in the background is the preferred method (less downtime). When you have enough storage controller cards populated in a machine, there might not be enough memory space to load the ROM. This results in a failure in the ability to boot, for the card which is "furthest" from the CPU socket. The BIOS loads those ROM images, and unnecessary parts of them "shrink", all in the name of making as much of the 256KB available as possible. For example, the video card can have a 64KB ROM on it. If you had several video cards, there might not be room to load anything else. So once I've entered Windows, the ROM is disabled and it's software controlled by the driver? Is there such a think as a RAID controller which doesn't do that? Even a "real" hardware RAID controller, like an Areca or a PERC, can have a BIOS page inserted. (One opened with ctrl-I or some other key combo.) The "real" hardware RAID allows setting up things at BIOS level too, just to get around some bootstrapping issues you might have. Once the handoff to the OS occurs, the OS driver talks to the real RAID hardware card. You use the "Management" control panel at that point, to set up RAID arrays, email yourself if the RAID array fails, and so on. The advantage of a real hardware RAID, is the transfer pattern (which chunks to read, the interleave order, the XOR step) is all done by the RAID card, without the OS doing anything to translate. The OS says "Read 0x1234" and the RAID card does the rest. Using scatter/gather DMA lists to load system RAM buffers with data from the resulting operation. On a "soft RAID", the driver in the OS does more monkey business, such as translating 0x1234 and some length field, into a sequence of reads or writes to individual disks. If the soft RAID was doing RAID5, then the processor would be asked to XOR blocks of data, using the ALU on the CPU and the XOR instruction. Which works, but might be limited to around 300MB/sec. Whereas a real hardware RAID card can do that at 2000MB/sec (probably limited today by PCIe bandwidth as much as anything). And real hardware RAID companies, it's their only business. Do a good job... or die. The companies making the soft RAID, don't take the job quite that seriously. You have to wait for them to fix stuff. Paul |
#7
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What is a "Softraid controller"?
On Fri, 25 May 2018 20:52:17 -0400, Paul
wrote: The "real" hardware RAID allows setting up things at BIOS level too, just to get around some bootstrapping issues you might have. Once the handoff to the OS occurs, the OS driver talks to the real RAID hardware card. You use the "Management" control panel at that point, to set up RAID arrays, email yourself if the RAID array fails, and so on. The advantage of a real hardware RAID, is the transfer pattern (which chunks to read, the interleave order, the XOR step) is all done by the RAID card, without the OS doing anything to translate. The OS says "Read 0x1234" and the RAID card does the rest. Using scatter/gather DMA lists to load system RAM buffers with data from the resulting operation. On a "soft RAID", the driver in the OS does more monkey business, such as translating 0x1234 and some length field, into a sequence of reads or writes to individual disks. If the soft RAID was doing RAID5, then the processor would be asked to XOR blocks of data, using the ALU on the CPU and the XOR instruction. Which works, but might be limited to around 300MB/sec. Whereas a real hardware RAID card can do that at 2000MB/sec (probably limited today by PCIe bandwidth as much as anything). Another factor I have found: If Windows blue screens and you have a software RAID the array is certain to be faulted and rebuild. I've never had any data problem from this but the machine runs pretty poorly while the rebuild is going on. Hardware RAID doesn't have this problem and if it has to rebuild doesn't dog the machine in the process. |
#8
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What is a "Softraid controller"?
On Sat, 26 May 2018 05:12:10 +0100, Loren Pechtel wrote:
On Fri, 25 May 2018 20:52:17 -0400, Paul wrote: The "real" hardware RAID allows setting up things at BIOS level too, just to get around some bootstrapping issues you might have. Once the handoff to the OS occurs, the OS driver talks to the real RAID hardware card. You use the "Management" control panel at that point, to set up RAID arrays, email yourself if the RAID array fails, and so on. The advantage of a real hardware RAID, is the transfer pattern (which chunks to read, the interleave order, the XOR step) is all done by the RAID card, without the OS doing anything to translate. The OS says "Read 0x1234" and the RAID card does the rest. Using scatter/gather DMA lists to load system RAM buffers with data from the resulting operation. On a "soft RAID", the driver in the OS does more monkey business, such as translating 0x1234 and some length field, into a sequence of reads or writes to individual disks. If the soft RAID was doing RAID5, then the processor would be asked to XOR blocks of data, using the ALU on the CPU and the XOR instruction. Which works, but might be limited to around 300MB/sec. Whereas a real hardware RAID card can do that at 2000MB/sec (probably limited today by PCIe bandwidth as much as anything). Another factor I have found: If Windows blue screens and you have a software RAID the array is certain to be faulted and rebuild. I've never had any data problem from this but the machine runs pretty poorly while the rebuild is going on. Hardware RAID doesn't have this problem and if it has to rebuild doesn't dog the machine in the process. Is my Intel on-motherboard (Gigabyte Z77-DS3H) RAID hard or soft? I don't find rebuilds slow the system much (although disk access is a bit slower than normal). A blue screen (does that happen much anymore?) will always cause a rebuild. CPU usage in normal use or during rebuild is virtually zero. A long time ago on a much older board I was annoyed to find that a 6 disk RAID was not a lot faster than a single drive. Presumably that was software and was limiting it. Mind you nowadays Intel seems to think Softraid isn't slow anymore. "Citing testing done by Tom's Hardware, Bobholz claimed that "Software RAID equals or outperforms hardware RAID these days. And this is because the host processors have gotten so much faster and you've got all the different cores going on."" -- You can make a signature quote seem authoritative by attributing it to a famous person. -- Sun Tzu |
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