Date: Fri, 29 Jan 2010 21:39:40 +0200 From: Nikos Vassiliadis <nvass9573@gmx.com> To: Adam Vande More <amvandemore@gmail.com> Cc: "freebsd-questions@FreeBSD.org" <freebsd-questions@freebsd.org> Subject: Re: gjournal on compact flash Message-ID: <4B63397C.2010408@gmx.com> In-Reply-To: <6201873e1001280851i726f7827p520f138ee84217d8@mail.gmail.com> References: <4B61BE70.1090109@gmx.com> <6201873e1001280851i726f7827p520f138ee84217d8@mail.gmail.com>
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On 1/28/2010 6:51 PM, Adam Vande More wrote: > On Thu, Jan 28, 2010 at 10:42 AM, Nikos Vassiliadis<nvass9573@gmx.com>wrote: > >> Hi, >> >> I am using a 40MB journal on a 500MB compact flash. >> Would that be sane, or I am causing more harm than >> good? >> >> My concerns are: >> 1) wear leveling. The journal is on specific part >> of the "disk" writing again and again. That >> should be handled by the CF itself. Though >> I am not sure it does a good job??? >> 2) I do care about ungraceful power cycles and I've seen >> posts on the net, mentioning: >> >>> More, If >>> you interrupt power at arbitrary times while the device is writing, >>> you can lose the integrity of the file system being modified. The loss >>> is not limited to the 512 byte sector being modified, as it generally >>> is with rotating disks; you can lose an entire erase block, maybe 64K >>> at once. >>> >> I guess the above comment renders the use >> of a journaling filesystem useless. But, doing >> some naive tests, power cycling the machine >> while writing and checksumming the data after >> fsck in preen mode, revealed no error. >> >> Thanks in advance for any insights, Nikos >> > > Soft Updates seem more appropriate for a 500MB CF drive than gjournal. > AFAIK, they are a wash in terms of reliability, and gjournal needs to write > all data twice meaning it's slower, and increases the wear on the drive. > The big drawback to soft updates is the fsck times after an unclean shutdown > which really shouldn't be an issue on a 500MB drive. > fsck time in my case is not an issue. What concerns me mostly is a situation where user intervention is required. The CF filesystem will be used in a embedded system and should work without user intervention. I too feel that geom journaling is not the best solution for my needs, but softupdates need more attention than gjournal. Perhaps, I should wait for SUJ, which will be in the tree soon. Nikos
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