[shell]: volume balance capacity by min volume density (#8026)

volume balance by min volume density and active volumes

weed/util/bytes.go

@@ -262,3 +262,5 @@ const (
 	PByte = TByte * 1000
 	EByte = PByte * 1000
 )
+
+const ErrVolumeNoSpaceLeft = "no space left for disk type"

weed/util/minfreespace.go

@@ -44,6 +44,20 @@ func (s MinFreeSpace) IsLow(freeBytes uint64, freePercent float32) (yes bool, de
 	return false, ""
 }
 
+func (s MinFreeSpace) AvailableSpace(freeBytes uint64, totalBytes uint64) uint64 {
+	var minFreeSpaceBytes uint64
+	switch s.Type {
+	case AsPercent:
+		minFreeSpaceBytes = uint64((float32(totalBytes) * s.Percent) / 100)
+	case AsBytes:
+		minFreeSpaceBytes = s.Bytes
+	}
+	if minFreeSpaceBytes > freeBytes {
+		return 0
+	}
+	return freeBytes - minFreeSpaceBytes
+}
+
 // String returns a string representation of MinFreeSpace.
 func (s MinFreeSpace) String() string {
 	switch s.Type {