Ulrich Windl wrote: > Hello, > > when browsing the open-iscsi feature list, I found: > - PDU header Digest; >
Is that from suse's docs or open-iscsi.orgs? > Does this mean that data digests are not supported? A bugzilla at readhat > near mid > of 2007 seems to confirm this. Data digests were working but when upstream did the scatterlist changes to the kernel it broke data digests. We have not found the cause yet. For Red Hat, they do not support them for different reasons depending on the version and arch. For example in RHEL5, the big endien crypto digest code is busted. It needs a fix from upstream, and I think in general there is still some other bugs in the digest code. > > I see the performance impact, but is there another reason against > implementing it? > Can I safely activate it on the target, or will it cause problems? > Another reason a lot of distros do not support it is because a common problem we always hit is that users will write out some data, then start modifying it again. But the kernel will normally not do do a sync write when you do a write. So once the write() returns, the kernel is still sending it through the caches, block, scsi, and iscsi layers. If you are writing to the data while the it is working its way through the iscsi layers, the iscsi layer could have done the digest calculation, then you could modify it and now when the target checks it the digest check will fail. And so this happens over and over and you get digest errors all over the place and the iscsi layers fire their error handling and retry and retry, and in the end they just say forget it and do not support data digests. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "open-iscsi" group. To post to this group, send email to open-iscsi@googlegroups.com To unsubscribe from this group, send email to open-iscsi+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/open-iscsi -~----------~----~----~----~------~----~------~--~---
