[CentOS] What FileSystems for large stores and very very large stores?

Fri Aug 9 20:56:34 UTC 2013
Eliezer Croitoru <eliezer at ngtech.co.il>

This was very helpful and I am testing something and writing on the
dovecot mailing list about it.


On 08/07/2013 09:42 PM, Matti Aarnio wrote:
> On 08/07/2013 03:58 AM, Eliezer Croitoru wrote:
>> OK so back to the issue in hands.
>> The issue is that I have a mail storage for more then 65k users per
>> domain and the ext4 doesn't support this size of directory list.
>> The reiser FS indeed fits for the purpose but ext4 doesn't even start to
>> scratch it.
>> Now the real question is that:
>> What FS will you use for dovecot backhand to store a domain with more
>> then 65k users?
>> Eliezer
> It was back in 1995 when I had this kind of problem with about 0.05 M
> accounts, and our solution was used until at least 0.5 M accounts, when
> I left the company. The filesystem in question back then degraded
> severely in performance when there were more than about 200 files in a
> directory.
> We ended up cooking our own way using FNV-1a hash, but Dovecot has
> something similar natively:
>     http://wiki2.dovecot.org/MailLocation
> The "Directory hashing" is the interesting part, although that
> explanation does look like needing a complete rewrite.
> Having lots of file names in directory will likely mean that a) your
> directory file is actually grown over time in small extents spanning all
> over the disk space and  b) thus its reading becomes very inefficient.
> Having a hashed subdirectory structure will mean that a 4kB file system
> block size will likely not overflow , or at most have only a few extend
> blocks, and their reading will not be _that_ much slower.
> Best Regards,  Matti Aarnio