Date: Mon, 31 Aug 2015 10:07:10 -0600 (MDT) From: Warren Block <wblock@wonkity.com> To: Quartz <quartz@sneakertech.com> Cc: freebsd-questions@freebsd.org Subject: Re: Replacing Drive with SSD Message-ID: <alpine.BSF.2.20.1508311000550.42983@wonkity.com> In-Reply-To: <55E45973.2050103@sneakertech.com> References: <CEAD84AD-341A-4FB9-A3A1-D0D5A550AFFD@lafn.org> <alpine.BSF.2.20.1508281235390.74312@wonkity.com> <20150829220311.c7608be1.freebsd@edvax.de> <alpine.BSF.2.20.1508300633160.44682@wonkity.com> <55E45973.2050103@sneakertech.com>
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On Mon, 31 Aug 2015, Quartz wrote: >> Making a partition for free space is one way. Another way is to leave >> part of the drive unpartitioned. Either one just guarantees there is a >> good supply of unused blocks available to the drive. > > I'm not super well versed on exactly how SSD TRIM works. How does the drive > in question know which blocks are or aren't free, isn't that a function of > the filesystem? For that matter, how does the drive even "know" which parts > are or aren't partitioned, it's not like they're programmed to understand MBR > vs GPT, etc. How does the system communicate to the drive firmware layer > which blocks are in use? That is exactly what TRIM is, a mechanism for a filesystem to tell the drive "this block is no longer in use". Otherwise, the only thing the drive has to determine whether a block is in use is whether it has ever been written. > Simply assuming based on if or how long ago it was written to can't > possibly be a workable solution. I'm not convinced that leaving large > chunks of the drive 'free' has any effect on wear leveling. It provides a pool of blocks that have not and will not be written.
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