From mboxrd@z Thu Jan 1 00:00:00 1970 From: "K. Richard Pixley" Subject: Re: snapshot limit? Date: Tue, 17 Aug 2010 11:40:11 -0700 Message-ID: <4C6AD78B.8070503@noir.com> References: <4C6AC9AC.9000503@noir.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: "linux-btrfs@vger.kernel.org" To: Dhiru Kholia Return-path: In-Reply-To: List-ID: On 8/17/10 11:05 , Dhiru Kholia wrote: > On Tue, Aug 17, 2010 at 10:41 AM, K. Richard Pixley > wrote: > > Is there a limit to the number of snapshots that can exist on a file > system > > concurrently? > > According to https://help.ubuntu.com/community/btrfs "You can create > as many subvolumes as you want, as long as you have storage capacity." > > -- > Cheers, > Dhiru > Yes. But if there's a limit to the number of paths that can point to a single file, then that's not strictly true. Rather, there's a limit based on the number of snapshots pointing to the same file. Since a snapshot is a copy of an existing file system, the only time a snapshot would not have files in common with previous snapshots would be in snapshots of empty file systems. Making snapshots of empty file systems begs the question of why one would be bothering with snapshots anyway. Hence, I suspect that in the vast majority of practical cases, there is indeed a current limit to the number of snapshots that can be made concurrently based on the limit to the number of paths to a single file. I was looking for validation of this theory and perhaps a way to detect, avoid, and/or recover from this situation. I'm experiencing at least one recurring error condition resulting in a polluted file system. I'm using a lot of snapshots in this particular application. So I'm wondering if such a limit exists and/or how to determine if I am running into this situation. Can anyone offer any clarification? --rich