Re: ext4 features

Trond Myklebust
2006-07-07T02:47:31Z

On Thu, 2006-07-06 at 22:42 -0400, Ric Wheeler wrote:

> The point of using checksums (or digital signatures on files) is to be
> able to detect when the on disk file has been corrupted - not to look
> for updates. With normal disks, even writes that are flagged as correct
> will occasionally actually end up corrupt on disk. The rate that you
> need to validate the checksums is not at a 4 time a day rate.
>
> Buying a nice, high array can make this much less of a concern, but
> those of us who get stuck using commodity disks should always have a way
> of detecting corruption and a backup (either on tape or on another box).

I repeat: you do _not_ need high res ctime/mtime updates in order to
figure out whether or not you need to do a daily backup on your file.
You do need it in order to figure out if the page you just read in from
your NFS server 2 microseconds ago is still valid.

Cheers,
Trond