Larry Dickson wrote: > With a 768 GB logical volume in a 2235 GB volume group, and 4 GB of > memory, I try to set up lots of snapshots (of 45 or 50 GB each) and > can't get past 15. Sometimes I'll succeed in generating more than 15 > COWs in /dev/mapper, but lvdisplay never shows more than 15 snapshots in > the "LV snapshot status source of" listing under the parent volume. I > searched and found 15 snapshots mentioned in a couple places like > wiki.samba.org/index.php/Shadow_Copies_with_Snapshots > <http://wiki.samba.org/index.php/Shadow_Copies_with_Snapshots> - but > nothing really authoritative. > > Is there really such a limit? Or is it a memory requirement - I seem to > remember so many MB memory per GB of storage, but can't find that > either. Versions are (variants of) lvm2-2.02.38, device-mapper-1.02.26, > kernel-smp-2.6.20 (64 bit). Hi, no, there is no hard limit for snapshots. But IIRC patches which solves some problems related with this (using private dm-io mempool) were commited in 2.6.22 kernel. But anyway, many snapshot from one origin causes serious performance degradation. (Current snapsot implementation is not ideal in this situation - every write to origin is replicated N-times to COW snapshot area - iow: every snapshot is independent and need copy changed area separately.) (But technically I tested >50 snapshot from one LV - should be limited only by available memory in recent kernels). Milan -- mbroz@redhat.com _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
