Re: [RFC] Checksum of the parity

2017-08-14 Thread Chris Murphy
On Mon, Aug 14, 2017 at 2:18 PM, Goffredo Baroncelli wrote: >> Anyway, I do wish I read the code better, so I knew exactly where, if >> at all, the RMW code was happening on disk rather than just in memory. >> There very clearly is RMW in memory code as a performanc

Re: [RFC] Checksum of the parity

2017-08-14 Thread Goffredo Baroncelli
On 08/14/2017 09:28 PM, Chris Murphy wrote: > On Mon, Aug 14, 2017 at 8:12 AM, Goffredo Baroncelli > wrote: >> On 08/13/2017 08:45 PM, Chris Murphy wrote: >>> [2] >>> Is Btrfs subject to the write hole problem manifesting on disk? I'm >>> not sure, sadly I don't read the code

Re: [RFC] Checksum of the parity

2017-08-14 Thread Chris Murphy
On Mon, Aug 14, 2017 at 8:12 AM, Goffredo Baroncelli wrote: > On 08/13/2017 08:45 PM, Chris Murphy wrote: >> [2] >> Is Btrfs subject to the write hole problem manifesting on disk? I'm >> not sure, sadly I don't read the code well enough. But if all Btrfs >> raid56 writes are

Re: [RFC] Checksum of the parity

2017-08-14 Thread Goffredo Baroncelli
On 08/13/2017 08:45 PM, Chris Murphy wrote: > [2] > Is Btrfs subject to the write hole problem manifesting on disk? I'm > not sure, sadly I don't read the code well enough. But if all Btrfs > raid56 writes are full stripe CoW writes, and if the prescribed order > guarantees still happen: data CoW

Re: [RFC] Checksum of the parity

2017-08-13 Thread Janos Toth F.
On Sun, Aug 13, 2017 at 8:45 PM, Chris Murphy wrote: > Further, the error detection of corrupt reconstruction is why I say > Btrfs is not subject *in practice* to the write hole problem. [2] > > [1] > I haven't tested the raid6 normal read case where a stripe contains >

Re: [RFC] Checksum of the parity

2017-08-13 Thread Chris Murphy
On Sun, Aug 13, 2017 at 8:16 AM, Goffredo Baroncelli wrote: > Hi all, > > in the BTRFS wiki, in the status page, in the "line" RAID5/6 it is reported > that the parity is not checksummed. This was reported several time in the ML > and also on other site (e.g. phoronix) as a

[RFC] Checksum of the parity

2017-08-13 Thread Goffredo Baroncelli
Hi all, in the BTRFS wiki, in the status page, in the "line" RAID5/6 it is reported that the parity is not checksummed. This was reported several time in the ML and also on other site (e.g. phoronix) as a BTRFS defect. However I was unable to understand it, and I am supposing that this is a