Date: Sun, 26 Aug 2018 10:42:13 -0700 From: bob prohaska <fbsd@www.zefox.net> To: Ian Lepore <ian@freebsd.org> Cc: Kirk McKusick <mckusick@mckusick.com>, FreeBSD Filesystems <freebsd-fs@FreeBSD.org>, freebsd-arm@freebsd.org, bob prohaska <fbsd@www.zefox.net> Subject: Re: CFT: TRIM Consolodation on UFS/FFS filesystems Message-ID: <20180826174213.GA15325@www.zefox.net> In-Reply-To: <1535127958.1488.31.camel@freebsd.org> References: <20180824000637.GA2157@www.zefox.net> <201808240027.w7O0Rh7f062555@chez.mckusick.com> <20180824161443.GB2157@www.zefox.net> <1535127958.1488.31.camel@freebsd.org>
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On Fri, Aug 24, 2018 at 10:25:58AM -0600, Ian Lepore wrote: > A usb sdcard reader/writer will definitely mask the trim capability of > an sdcard. Aside from that, ALL sdcards support trim on freebsd, > regardless of what any support folks at sandisk might tell you. The > trim operation is supported in the mmcsd driver by issuing sd erase > commands (CMD32/33/38 sequence) which has been in the sd spec from the > beginning. > > That said, it's my experience that different cards implement CMD38 > different ways. Some cards treat it like a TRIM -- it's a hint that > tells the card "the data in these sectors need not be preserved during > future updates to the erase block they're embedded in", and thus they > happen very fast and improve efficiency. Other cards treat it as a more > synchronous operation, physically erasing the blocks involved while- > you-wait, which can be *horrible* for performance on ufs (although > potentially it might get better with the consolidation of BIO_DELETEs). This raises a practical question: How does throughput to microSD compare to throughput to USB, assuming the flash controllers are well-executed? Sizewise there's no need for two devices, a single microSD has plenty of space for my purposes. I thought that having a separate device for swap and maybe /usr would speed things up, but perhaps that's quaint notion leftover from st506 days. Thanks for reading! bob prohaska
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