thex
Dabbler
- Joined
- Apr 3, 2023
- Messages
- 14
Short question to the experts.
Is my understanding correct that there is no possibility to add a "real" write cache to truenas(zfs)? With "real" meaning that it caches the actual data before writing it over to the slow spinning disks (not "just" indexes/metadata).
Background: Was dumb some years ago and have some SMR drives which I use with ZFS. Performance really tanks as expected when the CMR cache is filled (123MBs down to 20-30MBs). As I also recently upgraded to 2.5G networking my idea was that I could maybe add a cache SSD instead of buying new (still relatively slow) CMR disks. Also I would hope that it also helps with CMR disks but with 2.5 Gbps I guess benefits would be negligible.
My current understanding is my best bet to achieve something like my idea is to have a ZIL on an SSD and switch over to ASYNC writes but that will only "save" one transaction so 5 seconds and basically is not caching but just making sure that the data is not lost on power failure despite the ASYNC write mode. So what I would need is that it can queue multiple transactions. (Maybe my understanding regarding transactions is not complete here)
Use case is transferring a large 50-100gb file (RAM will not be sufficient for caching)
Thanks
Is my understanding correct that there is no possibility to add a "real" write cache to truenas(zfs)? With "real" meaning that it caches the actual data before writing it over to the slow spinning disks (not "just" indexes/metadata).
Background: Was dumb some years ago and have some SMR drives which I use with ZFS. Performance really tanks as expected when the CMR cache is filled (123MBs down to 20-30MBs). As I also recently upgraded to 2.5G networking my idea was that I could maybe add a cache SSD instead of buying new (still relatively slow) CMR disks. Also I would hope that it also helps with CMR disks but with 2.5 Gbps I guess benefits would be negligible.
My current understanding is my best bet to achieve something like my idea is to have a ZIL on an SSD and switch over to ASYNC writes but that will only "save" one transaction so 5 seconds and basically is not caching but just making sure that the data is not lost on power failure despite the ASYNC write mode. So what I would need is that it can queue multiple transactions. (Maybe my understanding regarding transactions is not complete here)
Use case is transferring a large 50-100gb file (RAM will not be sufficient for caching)
Thanks