On Fri, 18 May 2018, Zdenek Kabelac wrote: > Dne 18.5.2018 v 01:36 Eric Wheeler napsal(a): > > Hello all, > > > > Is there a technical reason that DATA_DEV_BLOCK_SIZE_MIN_SECTORS is > > limited to 64k? > > > > I realize that the metadata limits the maximum mappable pool size, so it > > needs to be bigger for big pools---but it is also the minimum COW size. > > > > Looking at the code this is enforced in pool_ctr() but isn't used anywhere > > else in the code. Is it strictly necessary to enforce this minimum? > > > > > Hi > > Selection of 64k was chosen as compromise between used space for metadada, > locking contention, kernel memory usage and overall speed performance. I understand the choice. What I am asking is this: would it be safe to let others make their own choice about block size provided they are warned about the metadata-chunk-size/pool-size limit tradeoff? If it is safe, can we relax the restriction? For example, 16k chunks still enables ~4TB pools, but with 1/4th of the CoW IO overhead on heavily snapshotted environments. -- Eric Wheeler > > > Regards > > Zdenek > > -- > dm-devel mailing list > dm-devel@xxxxxxxxxx > https://www.redhat.com/mailman/listinfo/dm-devel > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
