Re: [PATCH for-next v5 0/7] On-Demand Paging on SoftRoCE

[Guoqing Jiang <guoqing.jiang@linux.dev>]

On 5/19/23 17:57, Daisuke Matsuda (Fujitsu) wrote:
> On Fri, May 19, 2023 3:42 PM Guoqing Jiang wrote:
>> Hello,
>>
>> On 5/18/23 16:21, Daisuke Matsuda wrote:
>>> [2] [PATCH for-next v3 0/7] On-Demand Paging on SoftRoCE
>>> https://lore.kernel.org/lkml/cover.1671772917.git.matsuda-daisuke@fujitsu.com/
>> Quote from above link
>>
>> "There is a problem that data on DAX-enabled filesystem cannot be
>> duplicated with
>> software RAID or other hardware methods."
>>
>> Could you elaborate a bit more about the problem or any links about it?
>> Thank you.
> I am not an expert of Pmems, but my understanding is as follows:
>
> Pmem (Persistent memory) is detected as memory device during boot process.
> Physical addresses are allocated to them just like other memory in DIMM slots,
> so system have to treat them differently from traditional storage devices like HDD/SSD.
>
> It may be technically possible to duplicate data using multiple Pmems, but the duplication
> is practically not useful. For traditional storage devices, you can hot-remove and hot-add
> them easily on failure. However, Pmems are not attached to hot-pluggable slots. You have
> to halt the system and open the cabinet to change out the Pmem. This means availability
> of the system is not improved with data duplication on the same host.

I guess pmem with block translation table type would be fine since it 
can be used
like normal storage device, but I am not pmem expert as well 😁.

Thanks,
Guoqing