ZFS is crash resistent.
This means that ZFS - a Copy on Write Filesystem is not corrupt after a crash during writes (unlike older filesystems). This does not mean that a VM or a database is consistent on a crash as ZFS uses up to 4 GB RAM as writecache for a better performance. Think of an accounting software where you put off an amount from one account and the system crashes prior you can add it to another account (money in data nirwana as the ramcache is lost on a crash).
ZFS offers sync write, a mechanism where every commited write is logged. On a crash the commited writes are done on next reboot to allow a database or VM to be consistent. Sadly sync write requires a log device with powerloss protection and ultra low latency for a good performance. In the past these log devices (slog) were expensive and despire slow compared to fast writes without sync.
The new Intel Optane is a game-changing technology. When you use them as an Slog, even sequential sync writes are nearly as fast as writes without sync. If you use Optane not for Slog but the pool itself, it opens a new performance level on small random writes and sequential writes. Even a filer with sync enabled is possible now. I am impressed!
See http://napp-it.org/doc/downloads/optane_slog_pool_performane.pdf
This means that ZFS - a Copy on Write Filesystem is not corrupt after a crash during writes (unlike older filesystems). This does not mean that a VM or a database is consistent on a crash as ZFS uses up to 4 GB RAM as writecache for a better performance. Think of an accounting software where you put off an amount from one account and the system crashes prior you can add it to another account (money in data nirwana as the ramcache is lost on a crash).
ZFS offers sync write, a mechanism where every commited write is logged. On a crash the commited writes are done on next reboot to allow a database or VM to be consistent. Sadly sync write requires a log device with powerloss protection and ultra low latency for a good performance. In the past these log devices (slog) were expensive and despire slow compared to fast writes without sync.
The new Intel Optane is a game-changing technology. When you use them as an Slog, even sequential sync writes are nearly as fast as writes without sync. If you use Optane not for Slog but the pool itself, it opens a new performance level on small random writes and sequential writes. Even a filer with sync enabled is possible now. I am impressed!
See http://napp-it.org/doc/downloads/optane_slog_pool_performane.pdf