Re: [TUHS] Is it time to resurrect the original dsw (delete with switches)?

On Thu, Sep 02, 2021 at 08:52:23AM -0700, Jon Steinhart wrote: First of all, I wouldn't worry too much about big disks "baking" while they are spinning. Google runs its disks hot, in data centers where the ambient air temperatures is at least 80 degrees Fahrenheit[1], and it's not alone; Dell said in 2012 that it would honor warranties for servers running in environments as hot as 115 degrees Fahrenheit[2]. [1] https://www.google.com/about/datacenters/efficiency/ [2] https://www.datacenterknowledge.com/archives/2012/03/23/too-hot-for-humans-… And of course, if the ambient *air* temperature is 80 degrees plus, you can just imagine the temperature at the hard drive. It's also true that a long time ago, disk drives had limited number of spin up/down cycles; this was in its spec sheet, and SMART would track the number of disk spinups. I had a laptop drive where I had configured the OS so it would spin down the drive after 30 seconds of idle, and I realized that after about 9 months, SMART stats had reported that I had used up almost 50% of the rated spin up/down cycles for a laptop drive. Needless to say, I backed of my agressive spindown policies. That being said, more modern HDD's have been designed for better power effiencies, with slower disk rotational speeds (which is probably fine for media disks, unless you are serving a large number of different video streams at the same time), and they are designed to allow for a much larger number of spindown cycles. Check your spec sheets, this will be listed as load/unload cycles, and it will typically be a number like 200,000, 300,000 or 600,000. If you're only spinning down the a few times a day, I suspect you'll be fine. Especially since if the disk dies due to a head crash or other head failure, it'll be a case of an obvious disk failure, not silent data corruption, and you can just pull your backups out of your fire safe. I don't personally have a lot of knowledge of how modern HDD's actually survive large numbers of load/unload cycles, because at $WORK we keep the disks spinning at all times. A disk provides value in two ways: bytes of storage, and I/O operations. And an idle disk means we're wasting part of its value it could be providing, and if the goal is to decrease the overall storage TCO, wasting IOPS is not a good thing[3]. Hence, we try to organize our data to keep all of the hard drives busy, by peanut-buttering the hot data across all of the disks in the cluster[4]. [3] https://research.google/pubs/pub44830/ [4] http://www.pdsw.org/pdsw-discs17/slides/PDSW-DISCS-Google-Keynote.pdf Hence, a spun-down disk is a disk which is frittering away the CapEx of the drive and a portion of the server cost to which the disk is attached. And if you can find useful work for that disk to do, it's way more valuable to keep it spun up even taking into account to the power and air-conditioning costs of the spinning drive. It should also be noted that modern HDD's now also have *write* limits[5], just like SSD's. This is especially true for technologies like HAMR --- where if you need to apply *heat* to write, that means additional thermal stress on the drive head when you write to a disk, but the write limits predate new technologies like HAMR and MAMR. [5] https://www.theregister.com/2016/05/03/when_did_hard_drives_get_workload_ra… HDD write limits has implications for systems that are using log structured storage, or other copy-on-write schemes, or systems that are moving data around to balance hot and cold data as described in the PDSW keynote. This is probably not an issue for home systems, but it's one of the things which keeps the storage space interesting. :-) - Ted P.S. I have a Synology NAS box, and I *do* let the disks spin down. Storage at the industrial scale is really different than storage at the personal scale. I do use RAID, but my backup strategy in extremis is encrypted backups uploaded to cloud storage (where I can take advantage of industrial-scale storage pricing).