Date: Sun, 17 Dec 2017 15:00:07 +0000 From: RW <rwmaillists@googlemail.com> To: freebsd-questions@freebsd.org Subject: Re: hd firecuda Message-ID: <20171217150007.642efc20@gumby.homeunix.com> In-Reply-To: <20171217194753.3ab59e6d.freebsd.ed.lists@sumeritec.com> References: <1513447749.62024.1.camel@yandex.com> <20171217112428.150d8041.freebsd.ed.lists@sumeritec.com> <20171217111319.6a1af590@gumby.homeunix.com> <20171217194753.3ab59e6d.freebsd.ed.lists@sumeritec.com>
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On Sun, 17 Dec 2017 19:47:53 +0800 Erich Dollansky wrote: > > My understanding is they weren't intended to work like that. The > > last I heard was that the SSD was divided into two, one part > > specifically speeds up booting, and the other part caches sectors > > where the head had to seek to access a small amount of data. > > how should a hard disk work? Data is written, data is read. > > How should this SSHD know where by boot-related data is stored? It knows when you boot, it knows the sequence of sectors that were accessed after boot and it can keep statistics about which are accessed on multiple boots. > Why should this disk waste SSD memory for data I need with FreeBSD > very rarely? The sole reason that the first generation of these device was developed was to speed-up the time to boot Windows. > It does not seem to me that it is like this. It's based on an article written a few of years ago by a development engineer. Things have probably moved on a bit, boot time is less important than it was, so they probably cache other frequently read sectors. > It is more likely that it uses the 8GB as a write cache. I think it's unlikely that 8GB of cMLC could survive 5 years of writes to a 2GB hard drive, and if it were designed to work that way I would expect the specs to have a write endurance limit. The article I read said that in stress tests no flash device had failed before the drive failed mechanically, which suggests that writes were very carefully controlled. Seagate's marketing cites faster booting and loading of applications/games; this relies on reading from persistent cache, not write caching.
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