A method of determining whether to use a repository to store updates during a resynchronisation, the method comprising the steps of: transferring writes to a primary storage to a secondary storage in a mirror copy relationship; establishing a logical copy of the secondary storage as of a point-in-time; storing writes to the secondary storage, received from the primary storage in a logical copy received during a logical copy duration after the point-in-time, in a repository that comprises less storage space than the secondary storage; suspending the transferring of writes to the secondary storage, wherein during the suspension writes to the primary storage are indicated in an out-of-synch data structure; in response to ending the suspension of the transferring of writes from the primary to the secondary storage, a secondary storage manager performs the method steps of: estimating whether the available storage space in the repository is sufficient to store the writes indicated in the out-of-synch data structure and new writes received at the primary storage while transferring the writes indicated in the out-of-synch data structure; wherein estimating whether the available storage space in the repository is sufficient further comprises: estimating a time to transfer all the writes indicated in the out-of-synch data structure taking into account a size of the writes indicated in the out-of-synch data structure and a rate at which the new writes are received at the primary storage while transferring all the writes indicated in the out-of-synch data structure after ending the suspension and determining whether the available storage space in the repository is sufficient to store the writes indicated in the out-of-synch data structure and the new writes received during the estimated time; using the repository to store data in the secondary storage as of the point-in-time that is to be updated by writes transferred from the primary storage following the ending of the suspension in response to determining that the available storage space in the repository is sufficient; and using a third storage equal in size to the secondary storage to store data in the secondary storage updated after the suspension in response to determining that the available storage space in the repository is not sufficient. transferring writes to a primary storage to a secondary storage in a mirror copy relationship; establishing a logical copy of the secondary storage as of a point-in-time; storing writes to the secondary storage, received from the primary storage in a logical copy received during a logical copy duration after the point-in-time, in a repository that comprises less storage space than the secondary storage; suspending the transferring of writes to the secondary storage, wherein during the suspension writes to the primary storage are indicated in an out-of-synch data structure; in response to ending the suspension of the transferring of writes from the primary to the secondary storage, a secondary storage manager performs the method steps of: estimating whether the available storage space in the repository is sufficient to store the writes indicated in the out-of-synch data structure and new writes received at the primary storage while transferring the writes indicated in the out-of-synch data structure; wherein estimating whether the available storage space in the repository is sufficient further comprises: estimating whether the available storage space in the repository is sufficient to store the writes indicated in the out-of-synch data structure and new writes received at the primary storage while transferring the writes indicated in the out-of-synch data structure; wherein estimating whether the available storage space in the repository is sufficient further comprises: estimating a time to transfer all the writes indicated in the out-of-synch data structure taking into account a size of the writes indicated in the out-of-synch data structure and a rate at which the new writes are received at the primary storage while transferring all the writes indicated in the out-of-synch data structure after ending the suspension and determining whether the available storage space in the repository is sufficient to store the writes indicated in the out-of-synch data structure and the new writes received during the estimated time; using the repository to store data in the secondary storage as of the point-in-time that is to be updated by writes transferred from the primary storage following the ending of the suspension in response to determining that the available storage space in the repository is sufficient; and using a third storage equal in size to the secondary storage to store data in the secondary storage updated after the suspension in response to determining that the available storage space in the repository is not sufficient.