I have a PostgreSQL server which occasionally hangs for a long time on writes to my hard disks. Sometimes the fsync system calls take more than two minutes to complete.
Now I am wondering if moving the database from an mdadm RAID-1 on two hard disks to an mdadm RAID-1 on two SSDs will improve performance.
I know that for random access reads an SSD will easily outperform a hard disk. But that is not very important to me as I have enough memory to cache the entire database multiple times over.
I also know that write performance on an SSD is not nearly as good as the read performance. But I don't know how it compares to write performance on a hard disk.
If I move the database to SSD, can I expect improved write performance? If this depends on which SSD I choose, which specs on the SSD are important for me to consider?