2 ms·
I would like to see an update for this for SSDs. The devices are black boxes of mystery, possibly likely to fail nearly simultaneously (at least in terms of bei
by angry_octet 6y ago
I would like to see an update for this for SSDs. The devices are black boxes of mystery, possibly likely to fail nearly simultaneously (at least in terms of being unable to write). Early on we left 20% if capacity unformatted to allow more wear leveling, but running them in RAID1 seemed both necessary and likely to cause synchronous errors. RAIDZ1 over three disks might be okay. Obviously huge R/W bandwidth so resilvering doesn't take long.
Also, it isn't mentioned, but having the ZIL on battery backed flash can give huge improvements in IOPS to anything, and is far more valuable than extra TB or spindles.
- Rafuino 6y agoBattery backed flash sounds like a huge PitA to deal with though. Where do you even get that?
- angry_octet 6y agoThe battery is on the HBA. If you lose power it will replay all uncommitted writes. Specifically, to the ZIL but for everything else too. (Originally these were batteries but they are mainly supercapacitors now.) Just saw this interesting SNIA presentation, which indicates that having NVDIMMs might be even better than NVMe for ZIL. https://www.snia.org/sites/default/files/SDC/2018/presentations/PM/Principe_Nick_Real-World_Performance_Advantages_of_NVDIMM_and_NVMe_A_Case_Study_with_OpenZFS.pdf https://www.snia.org/sites/default/files/SDC/2018/presentati... NVDIMM as RAM+FLASH+capacitor: https://www.vikingtechnology.com/products/nvdimm/ https://www.vikingtechnology.com/products/nvdimm/