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Even SATA/SAS SSDs are much slower than NVM SSDs, and some of them are not much better than HDDs at doing journaling writes, which are sequential, very small requests, and have to be committed to persistent storage immediately. Some NVM SSDs can do journaling writes 1-2 orders of magnitude faster than SATA/SAS SSDs. So I could see using an NVM SSD as an SSD journal for SATA/SAS OSDs. However, if you have many SATA/SAS SSDs per host (e.g. > 10), I'm guessing that you might be better off with co-located journals since at that point the NVM SSD may be more likely to become a bottleneck, depending on the workload.