// Fetch buffer for I/O, returns from the pool if not allocates a new one and returns.
	var buffer []byte
	switch size := data.Size(); {
	case size == 0:
		buffer = make([]byte, 1) // Allocate at least a byte to reach EOF
	case size >= fi.Erasure.BlockSize:
		buffer = globalBytePoolCap.Load().Get()
		defer globalBytePoolCap.Load().Put(buffer)
	case size < fi.Erasure.BlockSize:

	serverPools.FilterMaxUsed(100 - (100 * diskReserveFraction))
	total := serverPools.TotalAvailable()
	if total == 0 {
		return -1
	}
	// choose when we reach this many
	choose := rand.Uint64() % total
	atTotal := uint64(0)
	for _, pool := range serverPools {
		atTotal += pool.Available
		if atTotal > choose && pool.Available > 0 {
			return pool.Index
		}
	}