docs: firmware upgrades on off2

docs/reports/2024-12-11-firmware-upgrade-on-off2.md

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+# 2024-12-11 Firmware upgrade on off2
+
+We noticed that on off2, the latency was really high for two of the hard drives,
+namely sdc and sdd.
+
+After some research, Christian found that it could be linked to an old firmware on the disks.
+
+## Preparation
+
+We can see firmware version by using (here for sdd):
+```bash
+smartctl -a /dev/sdd|grep -i firmware
+```
+It was `GB01` on the two culprits, while it was `GB03` on the others.
+
+Christian downloaded the firmware update for the disks,
+it comes as an installer: `Serial-ATA_Firmware_0942Y_LN_GB03_A00.BIN`
+
+You can find it by using the "Device Model" entry from `smartctl -a` (here `TOSHIBA MG07ACA14TEY`)
+and search for firmwaon the flyre. You land on `https://www.dell.com/support/home/fr-fr/drivers/driversdetails?driverid=0942y`
+
+
+## Changing the firmware
+
+The firmware update is happening on all disk on the server.
+
+We just run the program as root and it went smoothly.
+
+But we wanted to be sure that the firmware upgrade was taken into account
+(we didn't have the time to wait for a check,
+and where not sure of the figure seen with `zpool iostat`).
+
+So we decided to remove and re-add the disks to the server.
+Because our ZFS is raidz we can remove one disk at a time without losing data,
+and because we will remove it only for a short period, re-silver will be fast.
+
+So we removed sdd from ZFS pools
+```bash
+zpool offline zfs-hdd sdd4
+# for rpool the name is different, but we can recognize thanks to the serial number (smartctl -a gives it)
+zpool offline rpool ata-TOSHIBA_MG07ACA14TEY_X8F0A0H8F9RG-part3
+```
+
+We unplugged the disk and plugged it back in.
+
+Then we re-added it to the ZFS pools:
+```bash
+zpool online zfs-hdd sdd4
+zpool online rpool ata-TOSHIBA_MG07ACA14TEY_X8F0A0H8F9RG-part3
+```
+
+We then wait for re-silver to be completed, zpool status displays if a resilver is in progress or done:
+```bash
+zpool status
+```
+It was almost instantaneous.
+
+We did the same operation for the other disk, `sdc`.
+
+Note: we did not offlined the disk from rpool because we forgot to do it. It went well the same,
+because ZFS was resilient enough and did the resilver automatically.
+
+
+## Result
+
+The result is easy to see in munin:
+
+![disk latency graph](./media/2024-12-11-munin-off2-latency-after-firmware-update.png)
+
+![disk usage graph](./media/2024-12-11-munin-off2-usage-after-firmware-update.png)