minio/cmd/erasure-healfile.go

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/*
* 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 cmd
import (
"fmt"
"hash"
"strings"
"github.com/minio/minio/pkg/errors"
)
// HealFile tries to reconstruct an erasure-coded file spread over all
// available disks. HealFile will read the valid parts of the file,
// reconstruct the missing data and write the reconstructed parts back
// to `staleDisks` at the destination `dstVol/dstPath/`. Parts are
// verified against the given BitrotAlgorithm and checksums.
//
// `staleDisks` is a slice of disks where each non-nil entry has stale
// or no data, and so will be healed.
//
// It is required that `s.disks` have a (read-quorum) majority of
// disks with valid data for healing to work.
//
// In addition, `staleDisks` and `s.disks` must have the same ordering
// of disks w.r.t. erasure coding of the object.
//
// Errors when writing to `staleDisks` are not propagated as long as
// writes succeed for at least one disk. This allows partial healing
// despite stale disks being faulty.
//
// It returns bitrot checksums for the non-nil staleDisks on which
// healing succeeded.
func (s ErasureStorage) HealFile(staleDisks []StorageAPI, volume, path string, blocksize int64,
dstVol, dstPath string, size int64, alg BitrotAlgorithm, checksums [][]byte) (
f ErasureFileInfo, err error) {
if !alg.Available() {
return f, errors.Trace(errBitrotHashAlgoInvalid)
}
// Initialization
f.Checksums = make([][]byte, len(s.disks))
hashers := make([]hash.Hash, len(s.disks))
verifiers := make([]*BitrotVerifier, len(s.disks))
for i, disk := range s.disks {
switch {
case staleDisks[i] != nil:
hashers[i] = alg.New()
case disk == nil:
// disregard unavailable disk
continue
default:
verifiers[i] = NewBitrotVerifier(alg, checksums[i])
}
}
writeErrors := make([]error, len(s.disks))
// Scan part files on disk, block-by-block reconstruct it and
// write to stale disks.
chunksize := getChunkSize(blocksize, s.dataBlocks)
blocks := make([][]byte, len(s.disks))
for i := range blocks {
blocks[i] = make([]byte, chunksize)
}
var chunkOffset, blockOffset int64
for ; blockOffset < size; blockOffset += blocksize {
// last iteration may have less than blocksize data
// left, so chunksize needs to be recomputed.
if size < blockOffset+blocksize {
blocksize = size - blockOffset
chunksize = getChunkSize(blocksize, s.dataBlocks)
for i := range blocks {
blocks[i] = blocks[i][:chunksize]
}
}
// read a chunk from each disk, until we have
// `s.dataBlocks` number of chunks set to non-nil in
// `blocks`
numReads := 0
for i, disk := range s.disks {
// skip reading from unavailable or stale disks
if disk == nil || staleDisks[i] != nil {
blocks[i] = blocks[i][:0] // mark shard as missing
continue
}
_, err = disk.ReadFile(volume, path, chunkOffset, blocks[i], verifiers[i])
if err != nil {
// LOG FIXME: add a conditional log
// for read failures, once per-disk
// per-function-invocation.
blocks[i] = blocks[i][:0] // mark shard as missing
continue
}
numReads++
if numReads == s.dataBlocks {
// we have enough data to reconstruct
// mark all other blocks as missing
for j := i + 1; j < len(blocks); j++ {
blocks[j] = blocks[j][:0] // mark shard as missing
}
break
}
}
// advance the chunk offset to prepare for next loop
// iteration
chunkOffset += chunksize
// reconstruct data - this computes all data and parity shards
if err = s.ErasureDecodeDataAndParityBlocks(blocks); err != nil {
return f, err
}
// write computed shards as chunks on file in each
// stale disk
writeSucceeded := false
for i, disk := range staleDisks {
// skip nil disk or disk that had error on
// previous write
if disk == nil || writeErrors[i] != nil {
continue
}
writeErrors[i] = disk.AppendFile(dstVol, dstPath, blocks[i])
if writeErrors[i] == nil {
hashers[i].Write(blocks[i])
writeSucceeded = true
}
}
// If all disks had write errors we quit.
if !writeSucceeded {
// build error from all write errors
return f, errors.Trace(joinWriteErrors(writeErrors))
}
}
// copy computed file hashes into output variable
f.Size = size
f.Algorithm = alg
for i, disk := range staleDisks {
if disk == nil || writeErrors[i] != nil {
continue
}
f.Checksums[i] = hashers[i].Sum(nil)
}
return f, nil
}
func joinWriteErrors(errs []error) error {
msgs := []string{}
for i, err := range errs {
if err == nil {
continue
}
msgs = append(msgs, fmt.Sprintf("disk %d: %v", i+1, err))
}
return fmt.Errorf("all stale disks had write errors during healing: %s",
strings.Join(msgs, ", "))
}