On Tue, Apr 13 at  9:52, Bob Friesenhahn wrote:
On Mon, 12 Apr 2010, Eric D. Mudama wrote:

The advantage of TRIM, even in high end SSDs, is that it allows you to
effectively have additional "considerable extra space" available to
the device for garbage collection and wear management when not all
sectors are in use on the device.

For most users, with anywhere from 5-15% of their device unused, this
difference is significant and can improve performance greatly in some
workloads.  Without TRIM, the device has no way to use this space for
anything but tracking the data that is no longer active.

Based on the above, I think TRIM has the potential to help every SSD,
not just the "cheap" SSDs.

It seems that the "above" was missing. What concrete evidence were you citing?

Nothing concrete.  Just makes sense to me that if ZFS has to work
harder to garbage collect as a pool approaches 100% full, so would
SSDs that use variants of CoW have to work harder to garbage collect
as they approach 100% written.

The purpose of TRIM is to tell the drive that some # of sectors are no
longer important so that it doesn't have to work as hard in its
internal garbage collection.

The value should be clearly demonstrated an fact (with many months of prototype testing with various devices) before the feature becomes a pervasive part of the operating system. Every article I have read about the value of TRIM is pure speculation.

Perhaps it will be found that TRIM has more value for SAN storage (to reclaim space for accounting purposes) than for SSDs.

Perhaps, but that's not my gut feel.  I believe it has real value for
users in enterprise type workloads where performance comes down to a
simple calculation of reserve area on the SSD.

--eric


--
Eric D. Mudama
edmud...@mail.bounceswoosh.org

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