Re: How many files to create in one directory?

Eric Sandeen
2014-01-27T18:02:44Z

On 1/27/14, 1:16 AM, Masato Minda wrote:
> Dear Ext4 Developer;
>
> I've copied the files from VxFS to EXT4, I saw the message “Directory
> index full!”. I've checked the search engine and found these mails.
>
> http://www.spinics.net/lists/linux-ext4/msg25058.html
> http://www.spinics.net/lists/linux-ext4/msg25069.html
>
> Our Ext4's block size was 1024. I've changed the block size from 1024 to
> 4096. Our problem was solved. But I have question.
>
> How many files to create in one directory in 4096 block size?
> I think that it is about 3 million files with perfect hashing.
>
> 16*(4096-16)/8*(4096-8)/8*3/4= 3M
>
> Is this correct?

It will depend on the length of the filenames. But by my calculations,
for average 28-char filenames, it's closer to 30 million.

There are (4096-32)/8 indices per block, or 508.
There are 2 levels, so 508*508=258064 leaf blocks.
The length of each record for 28 char names would be 32 bytes.
So you can fit 4096/32 = 128 entries per leaf block.
258064 leaf blocks * 128 entries/bock is 33,032,192 entries.

I recently made a spreadsheet to calculate this.
I'm not sure if I am doing google docs sharing and protection
correctly, but this might work:

https://docs.google.com/spreadsheet/ccc?key=0AtdHTZsZ8XoYdE1IUXlDb1RXQkdPM3F4YWpfNGhMbFE&usp=sharing#gid=0

-Eric

> Thanks in advance.
>
> --
> Masato minmin Minda <minmin@jprs.co.jp>
> Japan Registry Services Co., Ltd. (JPRS)
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html