How many Rsync’s are doing at a time? If it is only a couple, you will not be able to take advantage of the full number of OSD’s, as each block of data is only located on 1 OSD (not including replicas). When you look at disk statistics you are seeing an average over time, so it will look like the OSD’s are not very busy, when in fact each one is busy for a very brief period. SSD journals will help your write latency, probably going down from around 15-30ms to under 5ms From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Piotr Wachowicz Is there any way to confirm (beforehand) that using SSDs for journals will help? We're wondering whether it makes sense to buy SSDs and put journals on them. But we're looking for a way to verify that this will actually help BEFORE we splash cash on SSDs. The problem is that the way we have things configured now, with journals on spinning HDDs (shared with OSDs as the backend storage), apart from slow read/write performance to Ceph I already mention, we're also seeing fairly low disk utilization on OSDs. This low disk utilization suggests that journals are not really used to their max, which begs for the questions whether buying SSDs for journals will help. This kind of suggests that the bottleneck is NOT the disk. But,m yeah, we cannot really confirm that. Our typical data access use case is a lot of small random read/writes. We're doing a lot of rsyncing (entire regular linux filesystems) from one VM to another. We're using Ceph for OpenStack storage (kvm). Enabling RBD cache didn't really help all that much. So, is there any way to confirm beforehand that using SSDs for journals will help in our case? Kind Regards, |
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