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Migrating to ZFS (self.linux)
submitted 11 months ago by sailingbythelee to c/linux
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I recently purchased a used PowerEdge R420 rack server with a Compellent SC220 Storage Shelf. I currently have four 3.5" HDDs in the R420 and ten 2.5" HDDs in the SC220. The R420 server previously had TrueNAS installed, so all of the hard drives on both the R420 and the SC220 are formatted with ZFS. I'm now running Ubuntu on the R420 using ZFS.

The server I'm replacing is an old gaming PC running Manjaro and BTRFS. It has one SSD with the operating system and two 4 TB HDDs set up as RAID0. I've been using the RAID to store media downloaded via the Servarr stack.

So, my goal is to create a large pool out of all of the HDDs (except the one running the OS) on the R420 and SC220, and then migrate the media data on the two 4 TB RAID0 drives on my old gaming PC over to R420/SC220 pool. I would then move my Servarr stack over to the R420 as well. Ideally, I'd also like to physically move the two 4 TB HDDs over to the R420. Presumably, I would have to reformat the drives to use ZFS rather the BTRFS and then integrate them somehow into the ZFS pool?

Anyway, I'm not sure of the best procedure to accomplish all of this, so I would be grateful to hear from anyone who has any experience or insight. Thanks in advance.

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[–] sailingbythelee 0 points 11 months ago (1 children)

Very interesting and thanks for helping me with this. I do have both SAS cables plugged in. I double-checked the back of the SC220 and I'm definitely only using the "A" ports. The lsblk command you suggested is interesting. Here is the output for the drives with two device letters.

first set of device letters* sde 8:64 0 931.5G 0 disk ST91000642SS ├─sde1 8:65 0 931.5G 0 part
└─sde9 8:73 0 8M 0 part
sdf 8:80 0 931.5G 0 disk ST91000642SS ├─sdf1 8:81 0 931.5G 0 part
└─sdf9 8:89 0 8M 0 part
sdg 8:96 0 838.4G 0 disk AL13SEB900 ├─sdg1 8:97 0 838.4G 0 part
└─sdg9 8:105 0 8M 0 part
sdh 8:112 0 838.4G 0 disk AL13SEB900 ├─sdh1 8:113 0 838.4G 0 part
└─sdh9 8:121 0 8M 0 part
sdi 8:128 0 931.5G 0 disk ST91000642SS ├─sdi1 8:129 0 931.5G 0 part
└─sdi9 8:137 0 8M 0 part
sdj 8:144 0 931.5G 0 disk ST91000642SS ├─sdj1 8:145 0 931.5G 0 part
└─sdj9 8:153 0 8M 0 part
sdk 8:160 0 931.5G 0 disk ST91000642SS ├─sdk1 8:161 0 931.5G 0 part
└─sdk9 8:169 0 8M 0 part
sdl 8:176 0 931.5G 0 disk ST91000642SS ├─sdl1 8:177 0 931.5G 0 part
└─sdl9 8:185 0 8M 0 part
sdm 8:192 0 838.4G 0 disk AL13SEB900 ├─sdm1 8:193 0 838.4G 0 part
└─sdm9 8:201 0 8M 0 part
sdn 8:208 0 931.5G 0 disk ST91000642SS ├─sdn1 8:209 0 931.5G 0 part
└─sdn9 8:217 0 8M 0 part

***** second set of device letters***** sdo 8:224 0 931.5G 0 disk ST91000642SS ├─sdo1 8:225 0 2G 0 part
└─sdo2 8:226 0 929.5G 0 part
sdp 8:240 0 931.5G 0 disk ST91000642SS ├─sdp1 8:241 0 2G 0 part
└─sdp2 8:242 0 929.5G 0 part
sdq 65:0 0 838.4G 0 disk AL13SEB900 ├─sdq1 65:1 0 2G 0 part
└─sdq2 65:2 0 836.4G 0 part
sdr 65:16 0 838.4G 0 disk AL13SEB900 ├─sdr1 65:17 0 2G 0 part
└─sdr2 65:18 0 836.4G 0 part
sds 65:32 0 931.5G 0 disk ST91000642SS ├─sds1 65:33 0 2G 0 part
└─sds2 65:34 0 929.5G 0 part
sdt 65:48 0 931.5G 0 disk ST91000642SS ├─sdt1 65:49 0 2G 0 part
└─sdt2 65:50 0 929.5G 0 part
sdu 65:64 0 931.5G 0 disk ST91000642SS ├─sdu1 65:65 0 2G 0 part
└─sdu2 65:66 0 929.5G 0 part
sdv 65:80 0 931.5G 0 disk ST91000642SS ├─sdv1 65:81 0 2G 0 part
└─sdv2 65:82 0 929.5G 0 part
sdw 65:96 0 838.4G 0 disk AL13SEB900 ├─sdw1 65:97 0 2G 0 part
└─sdw2 65:98 0 836.4G 0 part
sdx 65:112 0 931.5G 0 disk ST91000642SS ├─sdx1 65:113 0 2G 0 part
└─sdx2 65:114 0 929.5G 0 part

The first set and the second set do show that they are assigned to the same device model, which makes sense since I can also see in the Gnome "Disks" app that each of these disks has two device letters (e.g. sde and sdo). However, the interesting thing I noticed in the output above is that the first set of device letters show the smaller partition as 8M in size and the second set of device letters show the smaller partition as 2G in size. I recall that when I first looked at the disks, before I started using zpool to experiment with creating pools, all of the drives in the SC220 had a 2G partition labeled "swap" (in the Gnome Disks app). After I created a zpool using devices sde-sdn, the devices in the zpool have a partition that is 8M in size. Now only the second set of devices (sdo-sdx) still have the 2G partition, which seems weird. Are there two partition tables?

[–] [email protected] 1 points 11 months ago (1 children)

datasheet for one of the drive models apparently these have a dual SAS interface, so what you are seing could be completely normal. i dont have any experience with this type of setup though.

btw you can uniquely identify partitions by using something like lsblk -o+PARTUUID,FSTYPE the partuuid should never repeat in the output even if the partition table was somehow used as a template (though "dd"ing from disk to disk will duplicate those of course)

also check out the "SERIAL" column for lsblk to uniquely identify the drives themselves.

[–] sailingbythelee 0 points 11 months ago

Thanks, you are incredibly helpful. The four HDDs in the R420 are SCSI drives, while the ones in the SC220 are SAS drives, and it is indeed the 10 SAS drives in the SC220 that have two device letters each. Wow, how about that. If this is the explanation for why there are two devices per drive, I see on the SAS wiki that it has something to do with: "SAS devices feature dual ports, allowing for redundant backplanes or multipath I/O; this feature is usually referred to as the dual-domain SAS."

That gives me plenty to go on for further online research. I was just getting crap search results before, but now I have a better idea what to search for. Thanks a lot!!