Using RAM instead of disk for build servers (was: Re: Build servers offline due to failed SSD)
balt at inside.net
Sun Mar 14 23:26:02 UTC 2021
thanks for your detailed response. I hadn't thought of some of the build
intricacies you mention. Let alone the upcoming silicon change and phasing
out of x86. Sounds like your approach is a good balance for longevity,
performance, and cost.
On Mon, 15 Mar 2021 at 09:38, Ryan Schmidt <ryandesign at macports.org> wrote:
> On Mar 14, 2021, at 06:11, Balthasar Indermuehle wrote:
> > I used to run mac servers in what now can only be described as the days
> of yore... when a 32GB RAM bank cost a lot more than a (spinning) disk -
> and those were expensive then too. SSDs were not here yet. I haven't
> checked pricing lately, but I'd think you could put 256GB of RAM into a
> server for probably about the same as a 1TB SSD, and that would offer
> plenty of build space when used as a RAM drive. And that space will not
> degrade over time (unlike the SSD). In terms of longevity, for a machine
> with such a singularly targeted use case, I'd seriously consider taking the
> expense now, and have a server that lives for another decade.
> Some pricing details:
> OWC sells 96 GB Xserve RAM for $270 and 48 GB for $160. 96 + 96 + 48 would
> be 240 GB for $700.
> Meanwhile, the 500 GB SSDs I've been putting in cost about $65 each. I've
> already put in three and still need one more to get rid of the hard drives
> in the fourth server, though I may get a 1 TB SSD for $120 to have some
> extra room.
> Note that the way our build system (using our mpbb build script) works is
> that all (or most) ports that exist are kept installed but deactivated.
> When a build request comes in, we first activate all of that port's
> dependencies, then we build and install and activate that port, then we
> deactivate all ports. "Activate" means extract the tbz2 file to disk and
> note it in the registry. "Deactivate" means delete the extracted files from
> disk and note it in the registry. So even if we move all port building to a
> RAM disk, which will undeniably be faster and reduce wear on the disk, it
> will not eliminate it completely, not by a long shot. Some ports have
> hundreds of dependencies. Activating and deactivating ports is a
> considerable portion of what our build machines spend their day doing.
> If we wanted to move that from SSD to RAM disk as well, that would mean
> putting MacPorts itself onto the RAM disk. We wouldn't have room on the RAM
> disk to keep all ports installed, so it would mean not keeping any ports
> installed, and instead installing them on demand and then uninstalling them
> (and maybe we would need to budget even more RAM for the RAM disk to
> accommodate both space needed for MacPorts and for the dependencies and for
> the build). That means downloading and verifying each port's tbz2 file from
> the packages web server for every port build. Even though we do have a
> local packages server, so that traffic would not have to go over the
> Internet, the server uses a hard disk based RAID which is not the fastest
> in the world, so this would cause additional delays, not to mention
> additional wear and tear on the RAID's disks.
> As far as longevity, the previous set of 3 500 GB SSDs I bought for these
> servers in 2016 lasted 4-5 years. They were rated for 150 TBW (terabytes
> written) and actually endured around 450 TBW by the time they failed, or 3
> times as long as they were expected to last. The new SSDs are rated for 300
> TBW, and if they also last 3 times longer than that, then they might last
> 8-10 years, by which time we might have completely abandoned Intel-based
> Macs and be totally switched over to Apple Silicon hardware and will have
> no use for the Xserves anymore.
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