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

[Guoqing Jiang]

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@xxxxxxxxxxx/
> > 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