freebsd-swap on ssd

[Ronald Klop]

On Fri, 17 Feb 2012 20:09:21 +0100, Alexander Best <arundel at freebsd.org>  
wrote:

> On Fri Feb 17 12, Julian Elischer wrote:
>> On 2/17/12 6:16 AM, Alexander Best wrote:
>> >hi there,
>> >
>> >putting a freebsd-ufs partition on an ssd isn't recommended, since the  
>> ufs
>> >structure (unlike zfs e.g.) requires certain data to be continuously
>> >written to
>> >a fixed location and thus will cause the ssd to quickly run out of
>> >write-cycles
>> >and die.
>> nonsense.
>> the SSD doesn't use the same flash for the same logical locatio each  
>> time!
>> it maps it to different locations each time.
>
> i simply repeated what kirk mckusick said in the SU+J introduction  
> video. he
> said for exactly this reason ufs should not be used on an ssd, since  
> stuff like
> inode entries live in a fixed location, whereas with zfs the ueberblock  
> can
> live in 128 locations. also in case of SU+J, where the journal only  
> takes up a
> very small part of the disk due to the fact that it's only tracking  
> metadata
> changes and isn't doing logging (like gjournal), there's also the chance  
> to run
> out of write-cycles.

A related question.
Does journaling make sense on a ssd? I don't think there is a write cache  
on the ssd.


Ronald.



>
> see: http://youtu.be/_NuhRkiInvA
>
> cheers.
> alex
>
>>
>> >but how about using a small ssd (approx. 10GB) as one entire  
>> freebsd-swap
>> >partition? will this make more sense, or are there certain structures
>> >within
>> >the freebsd-swap partition type, which also need to be continuously
>> >written to
>> >a fixed location?
>> small SSDs may have less wear resistance than big ones..   the cheap
>> ones may not even
>> use proper mapping..
>> >another question i'd like to ask: are there also issues with  
>> read-cycles on
>> >ssds? because i was thinking about putting a freebsd-boot partition on  
>> an
>> >ssd
>> >drive and only mounting it ro. this should solve the write-cycle issue  
>> in
>> >theory. however i'm not sure, if stuff like the dirty bit or the ufs  
>> label
>> >will
>> >also remain untouched. so even though the partition will only be  
>> mounted
>> >ro,
>> >freebsd might still frequently write certain data to a fixed location  
>> on
>> >the
>> >ssd drive which hosts the freebsd-boot partition. if this is the case,  
>> is
>> >there
>> >a way of completely prohibiting any writes to a disk? will revoking any
>> >write
>> >permissions from the device entry under /dev guarantee this, or is  
>> using a
>> >any
>> >device 100% ro under freebsd impossible (unless it has a hardware  
>> switch to
>> >forbid writes)?
>>
>> yes there are small issues with read cycles but it is all hidden from
>> you by the drive.
>> >cheers.
>> >alex
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