XL: GetObject caching implemented for XL. (#2017)

The object cache implementation is XL cache, which defaults
to 8GB worth of read cache. Currently GetObject() transparently
writes to this cache upon first client read and then subsequently
serves reads from the same cache.

Currently expiration is not implemented.

xl-v1-errors.go

@@ -0,0 +1,37 @@
+/*
+ * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package main
+
+import "errors"
+
+// errXLMaxDisks - returned for reached maximum of disks.
+var errXLMaxDisks = errors.New("Number of disks are higher than supported maximum count '16'")
+
+// errXLMinDisks - returned for minimum number of disks.
+var errXLMinDisks = errors.New("Minimum '6' disks are required to enable erasure code")
+
+// errXLNumDisks - returned for odd number of disks.
+var errXLNumDisks = errors.New("Total number of disks should be multiples of '2'")
+
+// errXLReadQuorum - did not meet read quorum.
+var errXLReadQuorum = errors.New("Read failed. Insufficient number of disks online")
+
+// errXLWriteQuorum - did not meet write quorum.
+var errXLWriteQuorum = errors.New("Write failed. Insufficient number of disks online")
+
+// errXLDataCorrupt - err data corrupt.
+var errXLDataCorrupt = errors.New("Data likely corrupted, read failed.")