```go
func getAvailablePoolIdx(ctx context.Context) int {
        serverPools := z.getServerPoolsAvailableSpace(ctx)
        total := serverPools.TotalAvailable()
        // choose when we reach this many
        choose := rand.Uint64() % total
        atTotal := uint64(0)
        for _, pool := range serverPools {
                atTotal += pool.Available

type poolAvailableSpace struct {
	Index      int
	Available  uint64 // in bytes
	MaxUsedPct int    // Used disk percentage of most filled disk, rounded down.
}

// TotalAvailable - total available space
func (p serverPoolsAvailableSpace) TotalAvailable() uint64 {
	total := uint64(0)
	for _, z := range p {
		total += z.Available
	}
	return total
}