I tried /etc/exports with /scratch *(rw) which inherently does sync and also with /scratch *(rw,async) and saw no difference in an rsync -progress for a single nfs file copy of a 5gb tar file which averaged 460 MB/sec (max burst of 480). I cannot get nfs v4.2 to work even though /cat proc/fs/nfsd/versions shows +4.2 but I don't know how much better nfs 4.2 could be over 4.1. by default NFS connects as sync under version 4.1 and protocol=tcp. Servers using self-encrypting SSD's or a few with Dell BOSS M.2 for the linux operating system going over 100gbps HDR infiniband. In the end of the day, don't bother with sync, it's most likely that you're fine with async.įor what it's worth, as of 2022 and RHEL 7.9 The worst scenario would be a process that makes a lot of changes to the same place with sync each of them hits the SSD, while with async (the default) the SSD won't see most of them due to the kernel buffering. As of the lifetime, the wisdom is still valid, since writing to a SSD a lot "wears" it off. SSD: I don't know how fast the SSD memory is compared to RAM memory, but certainly it is not faster, so sync is likely to give a performance penalty, although not as bad as with mechanical disk drives. (If something goes wrong, then close() returns -1 with errno = EIO.) In contrast, with async the system buffers the write operation and optimizes the actual writes meanwhile, instead of being blocked the process in userland continues to run. For mechanical drives that means a huge slow down since the system has to move the disk heads to the right position with sync the userland process has to wait for the operation to complete.
The option sync means that all changes to the according filesystem are immediately flushed to disk the respective write operations are being waited for. async is the default, you don't need to specify that explicitly. So if my /dev/sda is SSD, should I - for the sake of reducing wear - add async option for / and /home file systems? Should I set sync or async option for additional partitions that I defined in my /etc/fstab? What is recommended approach for SSD and HDD drives?Īsync is the opposite of sync, which is rarely used.
# swap was on /dev/sda4 during installation # /home was on /dev/sda3 during installation Here is my /etc/fstab, I added some additional lines (see comment), but not changed anything in lines made by installer: # / was on /dev/sda2 during installation Ubuntu installer (14.04) have not specified sync nor async option for / partition, but have set async for /home by the option defaults.
Anyway this concerns me a bit, because my primary hard drive, where partitions / and /home are placed, is SSD drive. Man mount says that sync option may reduce lifetime of flash memory, but it may by obsolete conventional wisdom. What is the difference between sync and async mount options from the end-user point of view? Is file system mounted with one of these options works faster than if mounted with another one? Which option is the default one, if none of them is set?
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