Comment Re:FreeBSD & Linux NFS performance (Score 2) 107
Are these performance penalty measurements derived from NFS read operations, write operations, or a mixture of the two? If NFS writes were involved in the measurement, there is a reason for the relatively poor measured performance of FreeBSD.
According to RFC1094, NFSv2 servers must commit data to nonvolatile storage before acknowledging that a block write request has completed successfully. Given the relatively small size of NFS blocks (8K or less for NFSv2), forcing a separate write/sync/acknowledge cycle for each block that is written can result in relatively poor NFS write performance.
There are several solutions to this problem. Linux (and some commercial UNIX variants) acknowledge NFS write operations without forcing a disk write and sync for each individual block. This is obviously somewhat more dangerous, but yields much better NFS write performance. Some vendors offer hardware add-ins (such as the PrestoServ board) that provide nonvolatile storage that can be written to faster than a disk.
NFS version 3 has much better support for asynchronous writes without resorting to such hacks. Hopefully, Linux NFS3 will be usable soon.
If you are willing to live with the risk of data not necessarily being written to disk on the server when clients think that it has been, you can force FreeBSD to acknowledge NFS writes asynchronously using the command
/sbin/sysctl -w vfs.nfs.async=1
Retrying the benchmark after configuring FreeBSD to act more like Linux may yield different results.
According to RFC1094, NFSv2 servers must commit data to nonvolatile storage before acknowledging that a block write request has completed successfully. Given the relatively small size of NFS blocks (8K or less for NFSv2), forcing a separate write/sync/acknowledge cycle for each block that is written can result in relatively poor NFS write performance.
There are several solutions to this problem. Linux (and some commercial UNIX variants) acknowledge NFS write operations without forcing a disk write and sync for each individual block. This is obviously somewhat more dangerous, but yields much better NFS write performance. Some vendors offer hardware add-ins (such as the PrestoServ board) that provide nonvolatile storage that can be written to faster than a disk.
NFS version 3 has much better support for asynchronous writes without resorting to such hacks. Hopefully, Linux NFS3 will be usable soon.
If you are willing to live with the risk of data not necessarily being written to disk on the server when clients think that it has been, you can force FreeBSD to acknowledge NFS writes asynchronously using the command
/sbin/sysctl -w vfs.nfs.async=1
Retrying the benchmark after configuring FreeBSD to act more like Linux may yield different results.
