> -----Original Message----- > From: Linux on 390 Port [mailto:[EMAIL PROTECTED] On > Behalf Of Fargusson.Alan > Sent: Tuesday, October 04, 2005 12:10 PM > To: [email protected] > Subject: Re: www.nilfs.org > > > I think this file system is designed for data warehousing, > and not for general file storage. The unfortunate term here > is log-structured. I think they mean this in a database log > sense and not in a journaling sense. Also note the term > lossless. This only makes sense if they mean that they never > delete any data. >
>From what I know (little) of a similarly named facility from STK, I don't think this is correct. What it appears, at first glance, to do is to never update a disk allocation "in place". Each file consists of "segments". I don't know exactly how the segments are linked together. Now, when data in a segment is updated, the segment is not rewritten "in place". Instead, the filesystem will allocate a new, unused, "segment" (as they call it) and write the updated "segment" data there. It will then update the pointers which pointed to the old segment to point to the new segment, in the appropriate order (possibly causing more segments to be updated and so written to a new, unused, location). What this means is if an operation is interrupted (like a power failure), then it is as if the update were never even attempted. I.e. the update does not appear until the data plus metadata is comitted. The last block to be updated is the superblock. It appears that the superblock stays in one place (which makes sense to me). The filesystem must be periodically "garbage collected" to find where the previous used and now unused segments are located. -- John McKown Senior Systems Programmer UICI Insurance Center Information Technology This message (including any attachments) contains confidential information intended for a specific individual and purpose, and its' content is protected by law. If you are not the intended recipient, you should delete this message and are hereby notified that any disclosure, copying, or distribution of this transmission, or taking any action based on it, is strictly prohibited. ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
