comments on newfs raw disk ? Safe ? (7 terabyte array)

Eric Anderson anderson at freebsd.org
Sat Feb 10 07:12:16 UTC 2007


On 02/09/07 18:05, Antony Mawer wrote:
> On 9/02/2007 3:38 AM, Eric Anderson wrote:
>>> Only "collateral" problems because of the partition size: a regular
>>> (non-softupdates) fsck will take a LONG time to finish and eat a LOT of
>>> memory while it's doing its stuff. You'll need a lot of swap space (1GB
>>> per TB? someone had empirical numbers on this, I'm sure) if you think
>>> you'll need to fsck it entirely. Creating snapshots will also take a
>>> long time on it, and you probably want to search the lists for
>>> recommendations about creating snapshots in a second level directory in
>>> order not to block the root directory. Related to this is
>>> background-fsck which works by creating snapshots, so you'll probably
>>> want to disable it.
>> I have 5 10Tb file systems (and some 2Tb ones, but who cares about those 
>> tiny things? :)), and I can tell you that an empty huge file system is 
>> pretty easily fsck-able, but a full one will kill you.  It greatly 
>> depends on how many files (inodes) you have used on the file system.  If 
>> you have a massive amount of small files, you'll be eating up a ton of 
>> memory.  My 'rule of thumb' for my data (which averages to about 
>> 16k/file) is 1G of memory for each 1Tb  of disk space used.  So, on a 
>> 10Tb file system, if I ever want the fsck to complete, I need an AMD64 
>> box with *at least* 10G of memory, plus a lot of time.  A *lot* of time. 
>>  By 'a lot', I mean anywhere from a day, to several days.
> 
> Has anyone looked at the changes in DragonFly that were made in the 1.8 
> release? I noticed the other day, reading the release notes 
> (http://www.dragonflybsd.org/community/release1_8.shtml) the point:
> 
> "Greatly reduce the memory allocated by fsck when fscking filesytems 
> with a huge number of directories (primarily mirors with lots of 
> hardlinked files). Otherwise fsck can run out of memory on such 
> filesystems."
> 
> Whether or not this helps in the general case, or only the scenario 
> described, I do not know... but it would be interesting for someone with 
> enough filesystem-foo to have a look at!
> 
> --Antony


I'll check that out - didn't know about it, thanks!

Eric


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