gjournal and TRIM: A safe combination?

[RW]

On Tue, 20 Oct 2015 19:33:13 -0500
Brandon J. Wandersee wrote:

> I've recently created several new UFS partitions on an SSD. I
> activated gjournal on the largest--about 200Gb in size

> 1. UFS with TRIM, but without journaling. Disk performance is
> maintained, but data is unprotected in the event of a crash.

UFS with soft-updates  is roughly equivalent to the the metadata
journalling used on most modern filesystems. 

Personally, I wouldn't use gjournal on an SSD for several reasons:

1. full data journalling doubles the writes with respect to basic UFS
and therefore halves the life of the device. SU by contrast presumably
reduces the total writes by rolling-up multiple metadata updates in
memory. 

2. the journal needs to be much larger than on an ordinary hard drive
because of the write speeds, which is wasteful.

3. I suspect gjournal has had very little use on SSDs, so there may be
SSD specific bugs.



I use gjournal with large partitions on spinning disks, and soft-updates
with foreground checks for my SSD and small partitions. I've never had
a problem with SUs with foreground checks.