refactor: rename MaxShardId to MaxShardCount for clarity

- Change from MaxShardId=31 to MaxShardCount=32
- Eliminates confusing +1 arithmetic (MaxShardId+1)
- More intuitive: MaxShardCount directly represents the limit

fix: support custom EC ratios beyond 14 shards in VolumeEcShardsToVolume

- Add MaxShardId constant (31, since ShardBits is uint32)
- Use MaxShardId+1 (32) instead of TotalShardsCount (14) for tempShards buffer
- Prevents panic when slicing for volumes with >14 total shards
- Critical fix for custom EC configurations like 20+10

weed/server/volume_grpc_erasure_coding.go

@@ -454,7 +454,8 @@ func (vs *VolumeServer) VolumeEcShardsToVolume(ctx context.Context, req *volume_
 	glog.V(0).Infof("VolumeEcShardsToVolume: %v", req)
 
 	// Collect all EC shards (NewEcVolume will load EC config from .vif into v.ECContext)
-	tempShards := make([]string, erasure_coding.TotalShardsCount)
+	// Use MaxShardCount (32) to support custom EC ratios up to 32 total shards
+	tempShards := make([]string, erasure_coding.MaxShardCount)
 	v, found := vs.store.CollectEcShards(needle.VolumeId(req.VolumeId), tempShards)
 	if !found {
 		return nil, fmt.Errorf("ec volume %d not found", req.VolumeId)

weed/storage/erasure_coding/ec_volume_info.go

@@ -118,6 +118,10 @@ func (ecInfo *EcVolumeInfo) ToVolumeEcShardInformationMessage() (ret *master_pb.
 
 type ShardBits uint32 // use bits to indicate the shard id, use 32 bits just for possible future extension
 
+const (
+	MaxShardCount = 32 // Maximum number of shards since ShardBits is uint32 (bits 0-31)
+)
+
 func (b ShardBits) AddShardId(id ShardId) ShardBits {
 	return b | (1 << id)
 }