Date: Thu, 9 Jan 2014 19:05:10 -0000 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Garrett Wollman" <wollman@csail.mit.edu> Cc: freebsd-scsi@freebsd.org Subject: Re: Attempting ATA TRIM on SAS devices? Message-ID: <8A5A4C9BC59E434289AF83B025F3380A@multiplay.co.uk> References: <21197.39676.138433.937002@khavrinen.csail.mit.edu><430F34AB88D44C4BAF31DDC7AD214137@multiplay.co.uk><21197.47504.93295.771468@khavrinen.csail.mit.edu><CE07448557D04B6DAD7A2A1636EC462A@multiplay.co.uk><21197.56484.67992.739053@khavrinen.csail.mit.edu><D05A3164F6D945619B62945B1C9CCC1A@multiplay.co.uk><21197.59350.752519.254639@khavrinen.csail.mit.edu><A87BDB528EC946A4B8D50F89FBBC76EA@multiplay.co.uk> <21198.60557.126129.808095@khavrinen.csail.mit.edu>
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----- Original Message -----
From: "Garrett Wollman"
> <<On Thu, 9 Jan 2014 00:14:02 -0000, "Steven Hartland" <killing@multiplay.co.uk> said:
>
>>> I'm not sure that that works, given that the zpool is auto-imported at
>>> boot time and I don't know which da units will be assigned to the SSDs
>>> in question (no way to pin them so far as I can tell). Does ZFS
>>> generate BIO_DELETE on the cache devices at any time other than pool
>>> import?
>
>> Yes on every delete,
>
> What do you mean by "on every delete"? Do you mean whenever a block
> is evicted from the L2ARC?
Only when space is freed, as a trim map is maintained and processed
after a period, so if the same block has already been reused it
will have been removed from the map and the trim doesn't take
place. This means L2ARC is processed slightly differently from normal
devices as ZFS tries to keep it as full as possible.
Regards
Steve
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