Alpine Linux Persistence and Storage Summit 2021

The Alpine Linux Persistence and Storage Summit (ALPSS) was back this year in October. Again, the program committee consisting of Christoph Hellwig, Johannes Thumshirn and our own Richard Weinberger did a great job in organizing the get-together of the Linux Kernel Storage community. Like previous times, it took place at Lizumer Hütte (roughly 2000m altitude!) in the Tuxer Alps in Tyrol, Austria.

ALPSS 2021 Snow Edition

Day 1: Pizza and Hiking

The conference started on Tuesday with a nice pre-conference lunch (Pizza) in Innsbruck. Afterward, we took Taxis to Lager Walchen in the Wattental. Then it was time for everybody to put on their rain-proof hiking gear and shoulder the rucksacks. We hiked up the Zirbenweg to the Lizumer Hütte, a small path with some nice views for taking photos. After some sweating and puffing, we arrived there roughly two hours later and were greeted by the lodge-keeper with great food and drinks.

Day 2: Storage mixed with Snow

The next day started with a lot of snow, a joint breakfast in the cozy common room, and of course the first talks. First off were Joel Colledge and Philipp Reisner from LINBIT with their talk on performance optimizations in the Distributed Replicated Storage System (DRDB). They showcased areas of DRDB where they have done or plan to do performance improvements. One area directed to more exotic storage hardware like Persistent memory (PMEM), and three general optimizations.

They were followed by Richard Weinberger with a talk about his side project MUSE. MUSE enables emulating Memory Technology Devices (MTD) in userspace using the FUSE interface. Until now we already had nandsim (CONFIG_MTD_NAND_NANDSIM) to emulate NAND chips, but MUSE gives a much more flexible and hackable approach. It also supports SPI NOR and other types of flash storage. This is especially helpful for us at sigma star gmbh when debugging NAND, MTD, or UBIFS issues for our customers. (Hint: keep a lookout for a future, dedicated post about MUSE here at the sigma star blog).

While it was still snowing heavily outside, we continued with two short talks by Hannes Reinecke from SUSE on NVMe over Fabrics in-band authentication and NVMe userspace events and interaction. Especially the talk on in-band authentication was truly interesting. Hannes explained how the NVMe 2.0 specification describes an authentication approach over TCP and how he implemented it for the Linux Kernel. This spiked some discussion since the approach seems to reinvent the wheel as it is very similar to TLS 1.3. More to the point, it is simply an ephemeral Diffie-Hellman exchange that results in a shared session key. According to Hannes, this session key is then not used any further, unless one also uses NVMe encryption, which is just plain TLS 1.3. The conclusion among the participants of ALPSS was that the current specification should probably be improved before it is ready for wider use.

After a short tea break (and more snow), we continued with two talks by Damien Le Moal from Western Digital on command duration limits and Multi-actuator HDDs. In his first talk, Damien described his experiments with high throughput while still minimizing command execution latency. He showed a more general approach called Command Duration Limits (CDL) which expands on the ATA NCQ IO priority feature common to many SATA hard disks. Where ATA NCQ IO priority is only available via ATA, CDL is usable for both ATA and SCSI. The general idea of CDL is to augment disk commands with time limits and a policy on what to do if any limit is exceeded. In his second talk, Damien showcased his findings on the performance of varying payloads on Multi-actuator HDDs.

Since it was still snowing a lot, hiking was canceled and the afternoon continued with BoFs and discussions on a multitude of storage topics. The evening concluded with great food, drinks, and loads of socializing.

Day 3: More Storage

The third day started with a presentation from Matias Bjørling on the current state of Zoned Namespace SSDs on Linux followed by a discussion about what kind of applications can benefit from ZNS. Right afterward, John Meneghini gave insights into his work on a technical proposal to improve NVMe abort (TP-4097). The presentation was closed by a lengthy discussion about whether an abort command should be executed on the admin queue or not.

After a short coffee break to finally wake up, Dennis Maisenbacher presented a novel approach to implementing a Flash Translation Layer (FTL) on top of zoned devices using a Linux device-mapper driver, DM-zap. Various developers in the audience got confused by the usage of the word block on his slides. A block can be seen as a 512b/4k sector unit of a hard disk or an erase block of a flash-based device. In the end, everyone agreed that Dennis had the best ASCII art graphics of all presenters so far. ;-) The next talk focused also on zoned devices. Christoph Hellwig showed his work on a virtual block device that allows random access to zones. The device format is log-structured and makes use of Log-Structured Merge (LSM) trees. During the break, Christoph did a demo of XFS running on top of his log-structured disk.

Keith Busch gave insights into his recent proposal on RAID support for zoned devices. A short discussion emerged whether it is good or not to utilize the page cache for this. Johannes Thumshirn closed the session with his idea on declustered parity RAID support on btrfs. This RAID mode allows arbitrarily sided disks in a RAID system.

With the weather still being bad, most attendees stayed inside and enjoyed the surprisingly well-working internet connection of the lodge. After another excellent dinner, various discussions emerged and ended not seldom in heated debates.

Finally, Hans Holmberg offered two bottles of excellent Champagner he carried himself up to the lodge to celebrate our long-awaited meetup.

Day 4: Back down and Farewells

The last day of ALPSS concluded with a last joint breakfast, packing rucksacks, and hiking back to the base. This time we took the road down to Lager Walchen which made the hike down a bit quicker and especially safer when there is snow. With everybody safe back in the valley, we said our farewells and made our way back home.

Like every time, ALPSS was a great mix of in-depth, to-the-point talks and discussions on the latest in Linux Storage and the breathtaking scenery of the Tyrolean Alps.