$NetBSD: storage,v 1.23 2017/10/31 19:03:32 jdolecek Exp $ NetBSD Storage Roadmap ====================== This is a small roadmap document, and deals with the storage and file systems side of the operating system. It discusses elements, projects, and goals that are under development or under discussion; and it is divided into three categories based on perceived priority. The following elements, projects, and goals are considered strategic priorities for the project: 1. Improving iscsi 2. nfsv4 support 3. A better journaling file system solution 4. Getting zfs working for real 5. Seamless full-disk encryption 6. Finish tls-maxphys The following elements, projects, and goals are not strategic priorities but are still important undertakings worth doing: 7. nvme support 8. lfs64 9. Per-process namespaces 10. lvm tidyup 11. Flash translation layer 12. Shingled disk support 13. ext3/ext4 support 14. Port hammer from Dragonfly 15. afs maintenance 16. execute-in-place 17. extended attributes for acl and capability storage The following elements, projects, and goals are perhaps less pressing; this doesn't mean one shouldn't work on them but the expected payoff is perhaps less than for other things: 18. coda maintenance Explanations ============ 1. Improving iscsi ------------------ Both the existing iscsi target and initiator are fairly bad code, and neither works terribly well. Fixing this is fairly important as iscsi is where it's at for remote block devices. Note that there appears to be no compelling reason to move the target to the kernel or otherwise make major architectural changes. - As of January 2017 nobody is known to be working on this. - There is currently no clear timeframe or release target. - Contact agc for further information. 2. nfsv4 support ---------------- nfsv4 is at this point the de facto standard for FS-level (as opposed to block-level) network volumes in production settings. The legacy nfs code currently in NetBSD only supports nfsv2 and nfsv3. The intended plan is to port FreeBSD's nfsv4 code, which also includes nfsv2 and nfsv3 support, and eventually transition to it completely, dropping our current nfs code. (Which is kind of a mess.) So far the only step that has been taken is to import the code from FreeBSD. The next step is to update that import (since it was done a while ago now) and then work on getting it to configure and compile. - As of January 2017 pgoyette has done a bit of prodding of the code recently, but otherwise nobody is working on this, and a volunteer to take charge and move it forward rapidly is urgently needed. - There is no clear timeframe or release target, although having an experimental version ready for -8 would be great. - Contact dholland for further information. 3. A better journaling file system solution ------------------------------------------- WAPBL, the journaling FFS that NetBSD rolled out some time back, has a critical problem: it does not address the historic ffs behavior of allowing stale on-disk data to leak into user files in crashes. And because it runs faster, this happens more often and with more data. This situation is both a correctness and a security liability. Fixing it has turned out to be difficult. It is not really clear what the best option at this point is: + Fixing WAPBL (e.g. to flush newly allocated/newly written blocks to disk early) has been examined by several people who know the code base and judged difficult. Also, some other problems have come to light more recently; e.g. PR 50725, and 45676. Still, it might be the best way forward. Some performance and stability issues were resolved in netbsd-8, and more work is planned. + There is another journaling FFS; the Harvard one done by Margo Seltzer's group some years back. We have a copy of this, but as it was written in BSD/OS circa 1999 it needs a lot of merging, and then will undoubtedly also need a certain amount of polishing to be ready for production use. It does record-based rather than block-based journaling and does not share the stale data problem. + We could bring back softupdates (in the softupdates-with-journaling form found today in FreeBSD) -- this code is even more complicated than the softupdates code we removed back in 2009, and it's not clear that it's any more robust either. However, it would solve the stale data problem if someone wanted to port it over. It isn't clear that this would be any less work than getting the Harvard journaling FFS running... or than writing a whole new file system either. + We could write a whole new journaling file system. (That is, not FFS. Doing a new journaling FFS implementation is probably not sensible relative to merging the Harvard journaling FFS.) This is a big project. Right now it is not clear which of these avenues is the best way forward. Given the general manpower shortage, it may be that the best way is whatever looks best to someone who wants to work on the problem. - There is no clear timeframe or release target; but given that WAPBL has been disabled by default for new installs in -7 this problem can reasonably be said to have become critical. - jdolecek fixed some WAPBL stability issues, that work is included in netbsd-8, could be possibly enough for making it default for new installs again; there is kern/47030 which seems to be triggered by WAPBL however - There has been some interest in the Harvard journaling FFS but no significant progress. Nobody is known to be working on or particularly interested in porting softupdates-with-journaling. And, while dholland has been mumbling for some time about a plan for a specific new file system to solve this problem, there isn't any realistic prospect of significant progress on that in the foreseeable future, and nobody else is known to have or be working on even that much. - Contact joerg, martin, or jdolecek regarding WAPBL; contact dholland regarding the Harvard journaling FFS. 4. Getting zfs working for real ------------------------------- ZFS has been almost working for years now. It is high time we got it really working. One of the things this entails is updating the ZFS code, as what we have is rather old. The Illumos version is probably what we want for this. - There has been intermittent work on zfs, but as of January 2017 nobody is known to be actively working on it - There is no clear timeframe or release target. - Contact riastradh or ?? for further information. 5. Seamless full-disk encryption -------------------------------- (This is only sort of a storage issue.) We have cgd, and it is believed to still be cryptographically suitable, at least for the time being. However, we don't have any of the following things: + An easy way to install a machine with full-disk encryption. It should really just be a checkbox item in sysinst, or not much more than that. + Ideally, also an easy way to turn on full-disk encryption for a machine that's already been installed, though this is harder. + A good story for booting off a disk that is otherwise encrypted; obviously one cannot encrypt the bootblocks, but it isn't clear where in boot the encrypted volume should take over, or how to make a best effort at protecting the unencrypted elements needed to boot. (At least, in the absence of something like UEFI secure boot combined with an cryptographic oracle to sign your bootloader image so UEFI will accept it.) There's also the question of how one runs cgdconfig(8) and where the cgdconfig binary comes from. + A reasonable way to handle volume passphrases. MacOS apparently uses login passwords for this (or as passphrases for secondary keys, or something) and this seems to work well enough apart from the somewhat surreal experience of sometimes having to log in twice. However, it will complicate the bootup story. Given the increasing regulatory-level importance of full-disk encryption, this is at least a de facto requirement for using NetBSD on laptops in many circumstances. - As of January 2017 nobody is known to be working on this. - There is no clear timeframe or release target. - Contact dholland for further information. 6. Finish tls-maxphys --------------------- The tls-maxphys branch changes MAXPHYS (the maximum size of a single I/O request) from a global fixed constant to a value that's probed separately for each particular I/O channel based on its capabilities. Large values are highly desirable for e.g. feeding large disk arrays and SSDs, but do not work with all hardware. The code is nearly done and just needs more testing and support in more drivers. - As of January 2017 nobody is known to be working on this. - There is no clear timeframe or release target. - Contact tls for further information. 7. nvme suppport ---------------- nvme ("NVM Express") is a hardware interface standard for PCI-attached SSDs. NetBSD now has a driver for these. Driver is now MPSAFE and uses bufq fcfs (i.e. no disksort()) already, so the most obvious software bottlenecks were treated. It still needs more testing on real hardware, and it may be good to investigate some further optimizations, such as DragonFly pbuf(9) or something similar. Semi-relatedly, it is also time for scsipi to become MPSAFE. - As of May 2016 a port of OpenBSD's driver has been commited. This will be in -8. - The nvme driver is a backend to ld(4) which is MPSAFE, but we still need to attend to I/O path bottlenecks. Better instrumentation is needed. - Flush cache commands via DIOCCACHESYNC currently doesn't wait for completion; it must not poll since that corrupts command queue, but it should use a condition variable to wait for the flush to actually finish - There is no clear timeframe or release target for these points. - Contact msaitoh or agc for further information. 8. lfs64 -------- LFS currently only supports volumes up to 2 TB. As LFS is of interest for use on shingled disks (which are larger than 2 TB) and also for use on disk arrays (ditto) this is something of a problem. A 64-bit version of LFS for large volumes is in the works. - dholland was working on this in fall 2015 but time to finish it dried up. - The goal now is to get a few remaining things done in time for 8.0 so it will at least be ready for experimental use there. - Responsible: dholland 9. Per-process namespaces ------------------------- Support for per-process variation of the file system namespace enables a number of things; more flexible chroots, for example, and also potentially more efficient pkgsrc builds. dholland thought up a somewhat hackish but low-footprint way to implement this, and has a preliminary implementation, but concluded the scheme was too fragile for production. A different approach is probably needed, although the existing code could be tidied up and committed if that seems desirable. - As of January 2017 nobody is working on this. - Contact: dholland 10. lvm tidyup -------------- [agc says someone should look at our lvm stuff; XXX fill this in] - As of January 2017 nobody is known to be working on this. - There is no clear timeframe or release target. - Contact agc for further information. 11. Flash translation layer --------------------------- SSDs ship with firmware called a "flash translation layer" that arbitrates between the block device software expects to see and the raw flash chips. FTLs handle wear leveling, lifetime management, and also internal caching, striping, and other performance concerns. While NetBSD has a file system for raw flash (chfs), it seems that given things NetBSD is often used for it ought to come with a flash translation layer as well. Note that this is an area where writing your own is probably a bad plan; it is a complicated area with a lot of prior art that's also reportedly full of patent mines. There are a couple of open FTL implementations that we might be able to import. - As of January 2017 nobody is known to be working on this. - There is no clear timeframe or release target. - Contact dholland for further information. 12. Shingled disk support ------------------------- Shingled disks (or more technically, disks with "shingled magnetic recording" or SMR) can only write whole tracks at once. Thus, to operate effectively they require translation support similar to the flash translation layers found in SSDs. The nature and structure of shingle translation layers is still being researched; however, at some point we will want to support these things in NetBSD. - As of 2016 one of dholland's coworkers was looking at this. - There is no clear timeframe or release target. - Contact dholland for further information. 13. ext3/ext4 support --------------------- We would like to be able to read and write Linux ext3fs and ext4fs volumes. (We can already read clean ext3fs volumes as they're the same as ext2fs, modulo volume features our ext2fs code does not support; but we can't write them.) Ideally someone would write ext3 and/or ext4 code, whether integrated with or separate from the ext2 code we already have. It might also make sense to port or wrap the Linux ext3 or ext4 code so it can be loaded as a GPL'd kernel module; it isn't clear if that would be more or less work than doing an implementation. Note however that implementing ext3 has already defeated several people; this is a harder project than it looks. - GSoc 2016 brought support for extents, and also ro support for dir hashes; jdolecek also implemented several frequently used ext4 features so most contemporary ext filesystems should be possible to mount read-write - still need rw dir_nhash and xattr (semi-easy), and eventually journalling (hard) - There is no clear timeframe or release target. - jdolecek is working on improving ext3/ext4 support (particularily journalling) 14. Port hammer from Dragonfly ------------------------------ While the motivation for and role of hammer isn't perhaps super persuasive, it would still be good to have it. Porting it from Dragonfly is probably not that painful (compared to, say, zfs) but as the Dragonfly and NetBSD VFS layers have diverged in different directions from the original 4.4BSD, may not be entirely trivial either. - As of January 2017 nobody is known to be working on this. - There is no clear timeframe or release target. - There probably isn't any particular person to contact; for VFS concerns contact dholland or hannken. 15. afs maintenance ------------------- AFS needs periodic care and feeding to continue working as NetBSD changes, because the kernel-level bits aren't kept in the NetBSD tree and don't get updated with other things. This is an ongoing issue that always seems to need more manpower than it gets. It might make sense to import some of the kernel AFS code, or maybe even just some of the glue layer that it uses, in order to keep it more current. - jakllsch sometimes works on this. - We would like every release to have working AFS by the time it's released. - Contact jakllsch or gendalia about AFS; for VFS concerns contact dholland or hannken. 16. execute-in-place -------------------- It is likely that the future includes non-volatile storage (so-called "nvram") that looks like RAM from the perspective of software. Most importantly: the storage is memory-mapped rather than looking like a disk controller. There are a number of things NetBSD ought to have to be ready for this, of which probably the most important is "execute-in-place": when an executable is run from such storage, and mapped into user memory with mmap, the storage hardware pages should be able to appear directly in user memory. Right now they get gratuitously copied into RAM, which is slow and wasteful. There are also other reasons (e.g. embedded device ROMs) to want execute-in- place support. Note that at the implementation level this is a UVM issue rather than strictly a storage issue. Also note that one does not need access to nvram hardware to work on this issue; given the performance profiles touted for nvram technologies, a plain RAM disk like md(4) is sufficient both structurally and for performance analysis. - As of January 2017 nobody is known to be working on this. Some time back, uebayasi wrote some preliminary patches, but they were rejected by the UVM maintainers. - There is no clear timeframe or release target. - Contact dholland for further information. 17. use extended attributes for ACL and capability storage ---------------------------------------------------------- Currently there is some support for extended attributes in ffs, but nothing really uses it. I would be nice if we came up with a standard format to store ACL's and capabilities like Linux has. The various tools must be modified to understand this and be able to copy them if requested. Also tools to manipulate the data will need to be written. 18. coda maintenance -------------------- Coda only sort of works. [And I think it's behind relative to upstream, or something of the sort; XXX fill this in.] Also the code appears to have an ugly incestuous relationship with FFS. This should really be cleaned up. That or maybe it's time to remove Coda. - As of January 2017 nobody is known to be working on this. - There is no clear timeframe or release target. - There isn't anyone in particular to contact. - Circa 2012 christos made it work read-write and split it into modules. Since then christos has not tested it. Alistair Crooks, David Holland Fri Nov 20 02:17:53 EST 2015 Sun May 1 16:50:42 EDT 2016 (some updates) Fri Jan 13 00:40:50 EST 2017 (some more updates)