1. A system, comprising: one or more computing devices configured to: implement a plurality of compute instances at a virtualized compute service of a provider network, wherein a block-level storage volume implemented at a block storage service of the provider network is programmatically attached for block-level network access by a particular compute instance of the plurality of compute instances, and wherein, in response to one or more block-level I/O requests to the block-level storage volume from the particular compute instance, data is transferred from an object at a storage repository service of the provider network to populate the block-level storage volume prior to at least a portion of the data then being provided from the block-level storage volume to the particular compute instance in response to the one or more block-level I/O requests; obtain, corresponding to a particular phase of program execution at the particular compute instance, an indication of one or more data transfers from the object at the storage repository service to the block storage service; generate, based at least in part on the indication of the one or more data transfers, a storage access profile associated with the particular phase at the particular compute instance; store the storage access profile; in response to a determination that the particular phase of program execution is to occur at a different compute instance of the provider network, identify at least a portion of an object indicated by the storage access profile to be pre-loaded to populate a different block-level storage volume attached to the different compute instance, wherein the storage access profile generated based on the particular phase of program execution at the particular compute instance is used to identify the portion of the object to be pre-loaded to the different block-level storage volume attached to the different compute instance; and transfer the at least a portion of the object to the different block-level storage volume.