but calculating/comparing yourself won't help much - if the code says the CRC is incorrect, your calculation will also show it's incorrect.. the CRC is calculated server side, so it's also not really possible that the client sent you a wrong checksum. is this for the new LVM datastore, or the ZFS one? if ZFS, does 'zfs scrub' show any errors?
if the blobs are uncompressed, you could also check their size compared to the index that references them.