gjournal on compact flash

[Nikos Vassiliadis]

On 1/28/2010 6:51 PM, Adam Vande More wrote:
> On Thu, Jan 28, 2010 at 10:42 AM, Nikos Vassiliadis<nvass9573 at 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