ZFS and NFS / on-disk-cache

In the FreeB­SD mail­inglists I stum­bled over  a post which refers to a blog-post which describes why ZFS seems to be slow (on Solaris).

In short: ZFS guar­an­tees that the NFS client does not expe­ri­ence silent cor­rup­tion of data (NFS serv­er crash and loss of data which is sup­posed to be already on disk for the client). A rec­om­men­da­tion is to enable the disk-cache for disks which are com­plete­ly used by ZFS, as ZFS (unlike UFS) is aware of disk-caches. This increas­es the per­for­mance to what UFS is deliv­er­ing in the NFS case.

There is no in-deep descrip­tion of what it means that ZFS is aware of disk-caches, but I think this is a ref­er­ence to the fact that ZFS is send­ing a flush com­mand to the disk at the right moments. Let­ting aside the fact that there are disks out there which lie to you about this (they tell the flush com­mand fin­ished when it is not), this would mean that this is sup­port­ed in FreeB­SD too.

So every­one who is cur­rent­ly dis­abling the ZIL to get bet­ter NFS per­for­mance (and accept silent data cor­rup­tion on the client side): move your zpool to ded­i­cat­ed (no oth­er real FS than ZFS, swap and dump devices are OK) disks (hon­est ones) and enable the disk-caches instead of dis­abling the ZIL.

I also rec­om­mend that peo­ple which have ZFS already on ded­i­cat­ed (and hon­est) disks have a look if the disk-caches are enabled.

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