Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On 09.07.2012 18:04, Sebastian Riemer wrote: > Hi all, > > we at ProfitBricks do virtual data centers and we've got a customer who > has built-up a DRBD 8.3.11 system inside his virtual data center. > Storage is connected via InfiniBand and SCSI RDMA Protocol (SRP), > presented as local storage in the VMs (VirtIO blk). Like with iSCSI and > iSER such connections have trouble with 4k synchronous reads. The > connection between VMs is done via VirtIO net but is also IB-based on > the physical layer. > > The IO request size detection worked - the customer can do up to 128 KiB > IO requests (not more because of the 128 KiB hashing functions) on > regular data. But everything which is related to sync or resync is at > only 4 KiB IO request size, verified by "blktrace". It is not a matter > of the syncer rate limit. He has put it to 1000 MB/s. He can be lucky > that he has 40 MB/s, because synchronous 4 KiB reads on 1 Gbit/s > Ethernet with iSCSI are at only 10 MB/s. > > Why does DRBD syncs and resyncs in only slow 4 KiB IO requests? Found the reason and the fix I guess: http://git.drbd.org/gitweb.cgi?p=drbd-8.3.git;a=commit;h=3a2911f0c7ab80d061a5a6878c95f6d731c98554 It will be in 8.3.14. Cheers, Sebastian