If its a problem of libvirt then no VM should be created But I can create small image upto 4GB diskspace. This means it has some link with "disk_available_least" in below table

nova hypervisor-show silpixa00397258
+---------------------------+------------------------------------------+
| Property                  | Value                                    |
+---------------------------+------------------------------------------+
| cpu_info_arch             | x86_64                                   |
| cpu_info_features         | ["pge", "avx", "xsaveopt", "clflush",    |
|                           | "sep", "rtm", "tsc_adjust", "vme",       |
|                           | "dtes64", "invpcid", "msr", "sse",       |
|                           | "xsave", "smap", "vmx", "erms", "xtpr",  |
|                           | "cmov", "hle", "smep", "nx", "est",      |
|                           | "pat", "monitor", "smx", "pbe", "lm",    |
|                           | "tsc", "adx", "3dnowprefetch", "fpu",    |
|                           | "syscall", "tm", "sse4.1", "fxsr",       |
|                           | "sse4.2", "pclmuldq", "pcid", "pae",     |
|                           | "pni", "tsc-deadline", "mmx", "osxsave", |
|                           | "cx8", "mce", "de", "tm2", "ht", "dca",  |
|                           | "lahf_lm", "abm", "rdseed", "popcnt",    |
|                           | "mca", "pdpe1gb", "apic", "fsgsbase",    |
|                           | "f16c", "pse", "ds", "invtsc",           |
|                           | "mbm_total", "aes", "avx2", "sse2",      |
|                           | "ss", "ds_cpl", "arat", "bmi1", "bmi2",  |
|                           | "acpi", "ssse3", "rdtscp", "mbm_local",  |
|                           | "cmt", "cx16", "pse36", "mtrr", "movbe", |
|                           | "pdcm", "fma", "rdrand", "x2apic"]       |
| cpu_info_model            | Broadwell                                |
| cpu_info_topology_cells   | 2                                        |
| cpu_info_topology_cores   | 22                                       |
| cpu_info_topology_sockets | 1                                        |
| cpu_info_topology_threads | 2                                        |
| cpu_info_vendor           | Intel                                    |
| current_workload          | 0                                        |
| disk_available_least      | 4                                        |
| free_disk_gb              | 271                                      |
| free_ram_mb               | 49461                                    |
| host_ip                   | 10.237.222.40                            |
| hypervisor_hostname       | silpixa00397258                          |
| hypervisor_type           | QEMU                                     |
| hypervisor_version        | 2008000                                  |
| id                        | 1                                        |
| local_gb                  | 394                                      |
| local_gb_used             | 182                                      |
| memory_mb                 | 64309                                    |
| memory_mb_used            | 27790                                    |
| running_vms               | 4                                        |
| service_disabled_reason   | None                                     |
| service_host              | silpixa00397258                          |
| service_id                | 11                                       |
| state                     | up                                       |
| status                    | enabled                                  |
| vcpus                     | 88                                       |
| vcpus_used                | 8                                        |
+---------------------------+------------------------------------------+