Messages in this thread | | | From | (H. Peter Anvin) | Subject | Re: Ext2fs and hashed table. | Date | 15 Jun 1997 22:31:14 GMT |
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Followup to: <Pine.SGI.3.96.970615201424.29339C-100000@odin> By author: Torbjorn Lindgren <tl@funcom.com> In newsgroup: linux.dev.kernel > > > > > > > I'd say "tries to handle"... gnu-tar can't distinguish between > > > > allocated blocks all zero and sparse holes. in case where it's > > > > important that some areas are really allocated, gnu-tar may break > > > > your files. might not be a common problem but tar just can't deal > > > > with sparse files perfectly; dump/restore can... > > > > > > > Why would that matter? > > Because: > > 1. The files may well not *fit* on the disk if they aren't sparse! Take a > couple sparse 2GB cores, which really take less than 100KB each, handled > properly... > > 2. The file might *have* to be sparse, otherwise it won't work (rather > uncommon, but it do exist).
[In case you weren't aware: GNU tar handles sparse files!]
True, but you're talking about the opposite case. The complaint was that GNU tar can't tell when a file has blocks allocated all-zero, i.e. is denser than it need be. My question is: why does *that* matter? It will not look for holes (last I checked) in a file that has no holes, so the argument that some files have to be 100% allocated doesn't matter...
> > I would argue that dump can't deal with *ANY* file perfectly, since it > > (in the typical configuration) is committing the utter no-no of > > reading a non-quiescent r/w mounted filesystem from the raw block > > device. > > At least it's *tries* to handle them, which is more than I would claim > tar/cpio et al tries to do :-) Yes, another approach would be better, but > there are lots of cases where tar/cpio isn't anywhere near enough. > > There *are* reasons why commercial UNIX backup systems doesn't usually use > the 'read the raw-device' approach (one of them is the porting nightmare), > but on the other hand the one's I know of does handle sparse files, it's > really a necessity for serious backups. > > Wonder what it would take to make Legato (Networker) or Spectra Logic > (Alexandria) to create a backup client for Linux. Both support SCO after > all. The best would be to get them to port the Server too, but that might > be considerably harder :-)
Legato *has* a Linux client, although it is unsupported. Of course, we had to abandon Legato here because of repeated, severe failures that Legato refused to give us competent help with.
-hpa -- PGP: 2047/2A960705 BA 03 D3 2C 14 A8 A8 BD 1E DF FE 69 EE 35 BD 74 See http://www.zytor.com/~hpa/ for web page and full PGP public key Always looking for a few good BOsFH. ** Linux - the OS of global cooperation I am Baha'i -- ask me about it or see http://www.bahai.org/
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