-// A Volume is an interface representing a Keep back-end storage unit:
-// for example, a single mounted disk, a RAID array, an Amazon S3 volume,
-// etc.
-
package main
import (
"time"
)
+// A Volume is an interface representing a Keep back-end storage unit:
+// for example, a single mounted disk, a RAID array, an Amazon S3 volume,
+// etc.
type Volume interface {
// Get a block. IFF the returned error is nil, the caller must
// put the returned slice back into the buffer pool when it's
// access log if the block is not found on any other volumes
// either).
//
- // If the data in the backing store is bigger than BLOCKSIZE,
+ // If the data in the backing store is bigger than BlockSize,
// Get is permitted to return an error without reading any of
// the data.
Get(loc string) ([]byte, error)
//
// loc is as described in Get.
//
- // len(block) is guaranteed to be between 0 and BLOCKSIZE.
+ // len(block) is guaranteed to be between 0 and BlockSize.
//
// If a block is already stored under the same name (loc) with
// different content, Put must either overwrite the existing
- // data with the new data or return a non-nil error.
+ // data with the new data or return a non-nil error. When
+ // overwriting existing data, it must never leave the storage
+ // device in an inconsistent state: a subsequent call to Get
+ // must return either the entire old block, the entire new
+ // block, or an error. (An implementation that cannot peform
+ // atomic updates must leave the old data alone and return an
+ // error.)
//
// Put also sets the timestamp for the given locator to the
// current time.
// loc is as described in Get.
//
// If the timestamp for the given locator is newer than
- // blob_signature_ttl, Delete must not delete the data.
+ // blobSignatureTTL, Delete must not delete the data.
//
// If a Delete operation overlaps with any Touch or Put
// operations on the same locator, the implementation must
// reliably or fail outright.
//
// Corollary: A successful Touch or Put guarantees a block
- // will not be deleted for at least blob_signature_ttl
+ // will not be deleted for at least blobSignatureTTL
// seconds.
Delete(loc string) error
// will fail because it is full, but Mtime or Delete can
// succeed -- then Writable should return false.
Writable() bool
+
+ // Replication returns the storage redundancy of the
+ // underlying device. It will be passed on to clients in
+ // responses to PUT requests.
+ Replication() int
}
// A VolumeManager tells callers which volumes can read, which volumes
counter uint32
}
+// MakeRRVolumeManager initializes RRVolumeManager
func MakeRRVolumeManager(volumes []Volume) *RRVolumeManager {
vm := &RRVolumeManager{}
for _, v := range volumes {
return vm
}
+// AllReadable returns an array of all readable volumes
func (vm *RRVolumeManager) AllReadable() []Volume {
return vm.readables
}
+// AllWritable returns an array of all writable volumes
func (vm *RRVolumeManager) AllWritable() []Volume {
return vm.writables
}
+// NextWritable returns the next writable
func (vm *RRVolumeManager) NextWritable() Volume {
if len(vm.writables) == 0 {
return nil
return vm.writables[i%uint32(len(vm.writables))]
}
+// Close the RRVolumeManager
func (vm *RRVolumeManager) Close() {
}
-// VolumeStatus
+// VolumeStatus provides status information of the volume consisting of:
// * mount_point
// * device_num (an integer identifying the underlying storage system)
// * bytes_free