Month: May 2020

Enlarge / WUHAN, May 15, 2020 - Residents take nucleic acid tests at a testing post set up at a primary school in Dongxihu District in Wuhan, central China's Hubei Province, May 15, 2020. Wuhan will arrange nucleic acid tests for all residents who have not been tested before, in order to better know the number of asymptomatic cases of the novel coronavirus. (credit: Getty | Xinhua News Agency )

When Chinese officials in the city of Wuhan discovered a cluster of just six COVID-19 cases around two weeks ago—the first cases there in more than a month—they quickly set an ambitious plan to test the entire city of roughly 11 million and crush a potential second wave of infection. And they initially planned to try to do it in just 10 days.

Ten days out, they nearly met that goal. Wuhan Municipal Health Commission swabbed more than 9 million residents and tested more than 6.5 million of those swabs for coronavirus genetic material between May 15 and May 24, according to state media.

Laboratories in the city went from conducting 46,000 tests a day to as many as 1.47 million in the screening sprint, according to The New York Times. The Times notes that in the US, New York tested 1.7 million people since March 4, a nearly three-month time frame, according to The Atlantic’s COVID Tracking Project.

Enlarge / I get anxious if I can't watch the blinkenlights in the big Terminal window in the background while the tests run. (credit: Jim Salter)

In earlier coverage pitting ZFS against Linux kernel RAID, some readers had some concerns that we had missed some tricks for mdraid tuning. In particular, Louwrentius wanted us to retest mdadm with bitmaps disabled, and targetnovember thought that perhaps XFS might outperform ext4.

Write intent bitmaps are an mdraid feature that allows disks that have dropped off and re-entered the array to resync rather than rebuild from scratch. The "age" of the bitmap on the returning disk is used to determine what data has been written in its absence—which allows it to be updated with the new data only, rather than rebuilt from scratch.

XFS and ext4 are simply two different filesystems. Ext4 is the default root filesystem on most distributions, and XFS is an enterprise heavy-hitter most commonly seen in arrays in the hundreds or even thousands of tebibytes. We tested both this time, with bitmap support disabled.