Messages in this thread | | | Date | Tue, 4 Mar 2003 13:30:20 +0400 | From | Vlad Harchev <> | Subject | Re: 2.4 and cryptofs on raid1 - what will be cached and how many times |
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On Tue, Mar 04, 2003 at 08:50:46AM +1100, Neil Brown wrote: > On Monday March 3, hvv@hippo.ru wrote: > > On Sun, Mar 02, 2003 at 02:56:34PM +0400, Vlad Harchev wrote: > > > Hello, > > > > > > Could you please answer the following question: > > > > > > Suppose we have a crypto filesystem on a raid1 array of 2 devices. What will > > > the kernel cache of fileystem data contain - encrypted data or not? Will is > > > be 2 copies of the same data in the cache or not? > > > > Sorry for confusion - of course I meant linux software raid here.. > > With raid1 has no effect on caching. Exactly the same data is cached > with raid1 as with as plain SCSI or IDE drive.
The question I asked is - will under the active usage there be exactly one copy of a file's data, or there will be N (where N is number of disks in raid1 array) copies in the cache? I.e. how optimal caching is performed?
> Raid5 is different. It has an extra cache of some of the data that > has been written-to or read-from the devices.
OK, thank you for pointing this.
> > > > > > Is there any way to force kernel to cache the same file data only once, and > > > keep it unencrypted (in cache)? > > > > > I suspect that depends of the details of the implementation of you > "crypto filesystem".
Sorry for confusion - I meant loopback-based crypto filesystem - e.g. loop-aes based (loop-aes.sourceforge.net) or CryptoAPI-based (www.kerneli.org) - both are loopback-based filesystem (one has to call losetup(8) to point out chipher, a password..) I'm getting an impression that the kernel cache will contain encrypted data in case loopback-based crypto filesystems are used just observing performance..
Thank you for the anwser! -- Best regards, -Vlad - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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