are pci-express ssd worth over sata?

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dan
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are pci-express ssd worth over sata?

Post by dan » Sat Mar 16, 2013 8:26 am

there are a couple of hugely expensive pci-express ssd as opposed to sata ssd

are they worth it?

i would think maybe in a few years pci express ssd will be more common

nutball
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Re: are pci-express ssd worth over sata?

Post by nutball » Sat Mar 16, 2013 8:54 am

dan wrote:are they worth it?
If your time is worth a lot of money, yes they are worth it.
i would think maybe in a few years pci express ssd will be more common
Possibly. I agree that in the future solid-state mass storage will move closer to the CPU in the future, and may even end up being mapped directly into the virtual address space. Whether this is via PCI-E or some other interface remains to be seen. There's a whole lot that will change, eg. the way that file systems work will need to be re-evaluated, etc.

dan
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Re: are pci-express ssd worth over sata?

Post by dan » Sat Mar 16, 2013 10:04 am

nutball wrote:
dan wrote:are they worth it?
If your time is worth a lot of money, yes they are worth it.
i would think maybe in a few years pci express ssd will be more common
Possibly. I agree that in the future solid-state mass storage will move closer to the CPU in the future, and may even end up being mapped directly into the virtual address space. Whether this is via PCI-E or some other interface remains to be seen. There's a whole lot that will change, eg. the way that file systems work will need to be re-evaluated, etc.
hi!
is pci ssd bootable? curious

is 1x pci big improvement over sata?

could ssd be engineered bootable cheaply on a 16x bus?

how would mapped directly into the virtual address space change things?

washu
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Re: are pci-express ssd worth over sata?

Post by washu » Sat Mar 16, 2013 11:23 am

dan wrote: hi!
is pci ssd bootable? curious
Depends on the SSD. Some are bootable and some are not.
is 1x pci big improvement over sata?
Depends on the exact system, but in most cases no. PCIe x1 is 250, 500 or 1000 MB/sec for version 1.0, 2.0 and 3.0 respectively. SATA is 150, 300 or 600 MB/sec for version 1, 2 and 3 respectively. The common case in modern desktops is PCIe 2.0 x1 slots with at least some SATA 3 ports, so SATA is faster in raw transfer. This of course assumes that the SSD is limited by the above speeds and is also ignoring latency which would be better on PCIe.
could ssd be engineered bootable cheaply on a 16x bus?
Depends on your definition of cheap. Sure it could be done, and has been. Most PCIe SSDs are just a bunch of normal SATA SSDs with a normal HBA chip all on one card. Effectively no different than a bunch of SSDs attached to a RAID card in RAID 0. There are some that are just flash controllers on the PCIe bus but they are less common.
how would mapped directly into the virtual address space change things?
That would change how the system "sees" the SSD dramatically. It would look like RAM except that it would not lose it's contents when the power was shut off . The CPU could read or write to it directly instead of through a controller. Software would likely make it appear as a normal drive to the OS and users.

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Re: are pci-express ssd worth over sata?

Post by CA_Steve » Sat Mar 16, 2013 11:45 am

dan wrote:there are a couple of hugely expensive pci-express ssd as opposed to sata ssd

are they worth it?
For a consumer? No. Does it matter if windows boots in 15 sec vs 15.1 sec? Same with nearly ever other consumer application.

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Re: are pci-express ssd worth over sata?

Post by nutball » Sat Mar 16, 2013 12:31 pm

dan wrote:how would mapped directly into the virtual address space change things?
Because files stop being files and become persistent in-memory data-structures. Mass storage becomes credibly treatable as another level in the memory hierarchy (L1+L2+LLC+DDR, etc), that doesn't need to be treated differently in the way it currently is.

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Re: are pci-express ssd worth over sata?

Post by Mats » Sat Mar 16, 2013 3:20 pm


dan
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Re: are pci-express ssd worth over sata?

Post by dan » Sat Mar 16, 2013 7:46 pm

washu wrote:
dan wrote: hi!
is pci ssd bootable? curious
Depends on the SSD. Some are bootable and some are not.
is 1x pci big improvement over sata?
Depends on the exact system, but in most cases no. PCIe x1 is 250, 500 or 1000 MB/sec for version 1.0, 2.0 and 3.0 respectively. SATA is 150, 300 or 600 MB/sec for version 1, 2 and 3 respectively. The common case in modern desktops is PCIe 2.0 x1 slots with at least some SATA 3 ports, so SATA is faster in raw transfer. This of course assumes that the SSD is limited by the above speeds and is also ignoring latency which would be better on PCIe.
could ssd be engineered bootable cheaply on a 16x bus?
Depends on your definition of cheap. Sure it could be done, and has been. Most PCIe SSDs are just a bunch of normal SATA SSDs with a normal HBA chip all on one card. Effectively no different than a bunch of SSDs attached to a RAID card in RAID 0. There are some that are just flash controllers on the PCIe bus but they are less common.
how would mapped directly into the virtual address space change things?
That would change how the system "sees" the SSD dramatically. It would look like RAM except that it would not lose it's contents when the power was shut off . The CPU could read or write to it directly instead of through a controller. Software would likely make it appear as a normal drive to the OS and users.
that's interesting. why not then make it part of the address space? does it matter if it is pci or sata?

dan
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Re: are pci-express ssd worth over sata?

Post by dan » Sat Mar 16, 2013 7:47 pm

nutball wrote:
dan wrote:how would mapped directly into the virtual address space change things?
Because files stop being files and become persistent in-memory data-structures. Mass storage becomes credibly treatable as another level in the memory hierarchy (L1+L2+LLC+DDR, etc), that doesn't need to be treated differently in the way it currently is.
how much would performance improve?

washu
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Re: are pci-express ssd worth over sata?

Post by washu » Sun Mar 17, 2013 12:29 pm

dan wrote: that's interesting. why not then make it part of the address space? does it matter if it is pci or sata?
Because PCs and most other current computers are designed around the fact that storage is not part of the address space. There are some computers that do have their storage setup in this way, but they are nothing like current PCs. It's certainly not impossible to do, but major changes to things like OSes would be needed.

It would also be practically useless on 32 bit systems and could in the future pose limits even on 64 bit ones. No current 64 bit system has a full 64 bit physical address space. While it may seem that 64 bits is way bigger than we would ever need, that was once said about 32 bits.

It would have to be PCI, as SATA does not map storage into the address space.
dan wrote: how much would performance improve?
It would depend entirely on the storage medium used. Just because in theory PCIe could transfer at 16 GB/sec (3.0 x16) doesn't mean there is a realistic storage device that could come close to that. For example, it would be theoretically possible to map an optical drive into the CPUs address space. That wouldn't magically make it fast.

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Re: are pci-express ssd worth over sata?

Post by dan » Sun Mar 17, 2013 3:48 pm

washu wrote:
dan wrote: that's interesting. why not then make it part of the address space? does it matter if it is pci or sata?
Because PCs and most other current computers are designed around the fact that storage is not part of the address space. There are some computers that do have their storage setup in this way, but they are nothing like current PCs. It's certainly not impossible to do, but major changes to things like OSes would be needed.

It would also be practically useless on 32 bit systems and could in the future pose limits even on 64 bit ones. No current 64 bit system has a full 64 bit physical address space. While it may seem that 64 bits is way bigger than we would ever need, that was once said about 32 bits.

It would have to be PCI, as SATA does not map storage into the address space.
dan wrote: how much would performance improve?
It would depend entirely on the storage medium used. Just because in theory PCIe could transfer at 16 GB/sec (3.0 x16) doesn't mean there is a realistic storage device that could come close to that. For example, it would be theoretically possible to map an optical drive into the CPUs address space. That wouldn't magically make it fast.

interesting

Spoon Boy
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Re: are pci-express ssd worth over sata?

Post by Spoon Boy » Sun Mar 17, 2013 5:36 pm

Like CA_Steve said and IMO PCIE SSD are not worth the money, but if you realy want one PCIe-based Vector SSD manages 1GB/s in transfer speeds.

But personally i would wait for SATA Express as Mats said, as this will raise the current ceiling of 0.6GB/s to 1GB/s as well as a host of other improvements aimed at the ever increasing popularity of SSD's. See SATA Express systems coming this year

Someone may need to correct me on this one.
But i think when SATA Express comes out it will enable manufactures to produce SSD that will connect directly to the PCIe bus, isn't the PCIe bus mapped to the address space ?

washu
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Re: are pci-express ssd worth over sata?

Post by washu » Sun Mar 17, 2013 6:17 pm

Spoon Boy wrote: Someone may need to correct me on this one.
But i think when SATA Express comes out it will enable manufactures to produce SSD that will connect directly to the PCIe bus, isn't the PCIe bus mapped to the address space ?
The PCIe bus is mapped into the processor's address space. However, it is my understanding that SATA Express will appear to the host as a SATA Controller (probably just AHCI) with an XX GB SSD attached. It will not be mapping all XX GB of storage space into the address space. As far as the system and OS are concerned it's just a faster SATA disk.

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Re: are pci-express ssd worth over sata?

Post by Spoon Boy » Sun Mar 17, 2013 11:16 pm

Is this not where NVMe comes in ? from my understanding there will be both normal (AHCI) SSD'd and NVMe drives that appear to the system as a PCIe connected device.

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Re: are pci-express ssd worth over sata?

Post by washu » Mon Mar 18, 2013 6:00 am

Spoon Boy wrote:Is this not where NVMe comes in ? from my understanding there will be both normal (AHCI) SSD'd and NVMe drives that appear to the system as a PCIe connected device.
NVMe is just an alternate to SATA express. It is supposedly optimized for flash memory but at the downside of not being SATA compatible thus needing new drivers. SATA Express in theory should "just work" as it uses the same commands as regular SATA. Both NVMe and SATA Express controllers will appear on the PCIe bus, but will not be mapping the storage space into the CPU address space.

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Re: are pci-express ssd worth over sata?

Post by nutball » Mon Mar 18, 2013 6:13 am


dan
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Re: are pci-express ssd worth over sata?

Post by dan » Mon Mar 18, 2013 6:24 am

ok sata express it is.

hard drive capacities seems to have stagnated and topped off at 1tb/platters
when or how soon will 2tb ssd be affordable?

Spoon Boy
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Re: are pci-express ssd worth over sata?

Post by Spoon Boy » Mon Mar 18, 2013 10:14 am

@washu, Ahhh ok i think i get it now. NVMe is a unified driver for PCIe cards so manufactures don't have to develop there own drivers.

@nutball, Nice find and a good read, Thanks.
So it looks like it maybe something for the future but not with Sata Express.

@dan, Depends what you call affordable, looking into my crystal ball :lol: i don't see SSD's dropping much under the £1 per MB.
But who really knows what the future holds. :?:

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