Hibernation or suspend to disk is the process of saving the contents of RAM to the disk. Compressing the memory and writing the data to disk can be a time consuming inefficient process. In modern workstations it is not uncommon to have hibernation files that are 80GB. Writing the hibernation file to HDDs that have a write performance range between 150MB/s to 225MB/s under ideal conditions can take several minutes.
Actual performance during a hibernation will be lower because the data being written to the drives is sent with a range of transfer sizes and may be sent single threaded.
Windows also has to stop processes to prevent them from modifying the memory during the hibernation process. This overhead may add a few minutes to the hibernation process. There may be noticeable moments of no disk activity at all.
Using optimized drive performance numbers without considering inefficiencies of having to stop processes in order to save their state and compress the memory results in 6 to 9 minutes to save 80GB to HDDs.
80000MB / 225MB/s / (60seconds/minute) = 6 minutes
80000MB / 150MB/s / (60seconds/minute) = 8.9 minutes
In the case of RAID 5 there is additional overhead for parity calculation that has to be performed by the CPU using a portion of reserved memory. Parity needs to be read, verified, recalculated, and written with every data write.
A simplified formula for write performance on RAID 5 is:
HDD_MB/s x #disks x 25%
HDD_MB/s x #disks x 25%
On a 3 HDD RAID 5 with 225MB/s HDDs write performance is expected to be:
225MB/s x 3 x .25 = 168MB/s
225MB/s x 3 x .25 = 168MB/s
To save the 80GB hibernate file it would take:
80000MB / 168MB/s / (60seconds/minute) = 7.9 minutes
80000MB / 168MB/s / (60seconds/minute) = 7.9 minutes
On a 3 HDD RAID 5 with 150MB/s HDDs write performance is expected to be:
150MB/s x 3 x .25 = 113MB/s
150MB/s x 3 x .25 = 113MB/s
To save the 80GB hibernate file we it would take:
80000MB / 113MB/s / (60seconds/minute) = 11.8 minutes
80000MB / 113MB/s / (60seconds/minute) = 11.8 minutes
Actual hibernation time will be longer with general Windows overhead adding a few minutes to the process.
Windows 10 has some improvements in the hibernate process but is still noticeably slow.
Systems with more DRAM will have longer hibernate times.
Different HDD models may result in approximately a 2 minute variation in hibernate time.
Mixing drive models in RAID 5 can reduce performance to the performance of the lowest performing drive in the RAID 5.
