Mounting an SSD

Question

Mounting an SSD

I have recently got a 'dedicated GAME server' from OVH and I've been promised 2x480GB SOFT SSDs.

However, df -h shows this output:

root@dedi:/home/shavit# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/root        20G  4.2G   14G  24% /
devtmpfs         63G  4.0K   63G   1% /dev
none            4.0K     0  4.0K   0% /sys/fs/cgroup
none             13G  868K   13G   1% /run
none            5.0M     0  5.0M   0% /run/lock
none             63G  1.1M   63G   1% /run/shm
none            100M     0  100M   0% /run/user
/dev/md2        421G  392G  7.5G  99% /home

I suppose that /dev/md2 is one of the 480GB SOFT SSDs I've been promised to have.
We're at 99% disk usage at this moment and are very scared of possible data loss, I'm afraid that we don't have the other disk mounted.

root@dedi:/home/shavit# fdisk -l

Disk /dev/sdb: 480.1 GB, 480103981056 bytes
255 heads, 63 sectors/track, 58369 cylinders, total 937703088 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x1768c0f0

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *        4096    40962047    20478976   fd  Linux RAID autodetect
/dev/sdb2        40962048   936648703   447843328   fd  Linux RAID autodetect
/dev/sdb3       936648704   937695231      523264   82  Linux swap / Solaris

Disk /dev/sda: 480.1 GB, 480103981056 bytes
255 heads, 63 sectors/track, 58369 cylinders, total 937703088 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x3767be62

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        4096    40962047    20478976   fd  Linux RAID autodetect
/dev/sda2        40962048   936648703   447843328   fd  Linux RAID autodetect
/dev/sda3       936648704   937695231      523264   82  Linux swap / Solaris

Disk /dev/md2: 458.6 GB, 458591502336 bytes
2 heads, 4 sectors/track, 111960816 cylinders, total 895686528 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/md2 doesn't contain a valid partition table

Disk /dev/md1: 21.0 GB, 20970405888 bytes
2 heads, 4 sectors/track, 5119728 cylinders, total 40957824 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/md1 doesn't contain a valid partition table

I'm a complete noob with everything related to system operating and as I said I'm afraid of losing data so I'd prefer to not mess with anything by myself as I don't have enough physical disk space on my PC to even backup data on.

Could anyone please help me mount the unmounted SSD without losing data? I feel lost.

Thanks!

Edit: cat /proc/mdstat

root@dedi:/home/shavit# cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] [multipath] [faulty]
md1 : active raid1 sda1[0] sdb1[1]
      20478912 blocks [2/2] [UU]

md2 : active raid1 sda2[0] sdb2[1]
      447843264 blocks [2/2] [UU]
      bitmap: 3/4 pages [12KB], 65536KB chunk

unused devices: <none>

cat /proc/swaps

root@dedi:/home/shavit# cat /proc/swaps
Filename                                Type            Size    Used    Priority
/dev/sdb3                               partition       523260  15476   -1
/dev/sda3                               partition       523260  0       -2

linux

mount

ssd

ovh

asked on Server Fault May 21, 2016 by

shavit • edited May 21, 2016 by

shavit

2 Answers

It's really hard to read your /proc/mdstat in a comment, but it shows that md1 is a raid1 array of sda1 and sdb1, and that md2 is a raid1 array of sda2 and sdb2. And the last two partitions are used for swap.

So you are using both discs.

I guess OVH set up like that because raid1 often gives more speed, and on game servers you typically want speed. - And considering how big a complany OVH is, it is probably documented on their site, that this is what you get.

answered on Server Fault May 21, 2016 by

Henrik • edited May 21, 2016 by

Henrik

Michael really got here first, and Henrik has already posted a perfectly good answer, but you still seem to have questions, so:

You have two 480GB SSDs. Each has been partitioned into three, /dev/sd[ab][123]. The two 1 partitions (20GB each) are mirrored as /dev/md1, which as the root file system on it. The two 2 partitions (around 450GB each) have been mirrored as /dev/md2, which has the /home file system; after conversion (binary vs denary), file system overhead, and reserved space, this translates to about 400GB usable. The two 3 partitions (of about half a gig each) have been made available as a striped swap device of total capacity about a gig.

This means that

You don't have any unused disc space. You can probably make a few more free gig on /home by tuning down the free space (tune2fs -m 2 /dev/md2), but apart from that, you need to tidy up /home to avoid filling it up.
If either SSD fails, the machine will almost instantly reboot (as half of swap will go away), but provided the boot blocks have all been set up correctly, it will reboot without any persistent data loss. This is a fairly normal way to set up a machine.
You could break the mirrors, and free up /dev/sdb for actual FS usage. This is fragile, I wouldn't choose to do it, and you're going to want to get an expert in to help you, but it's an option if you must have more disc space right now, and you have no other options.

answered on Server Fault May 21, 2016 by

MadHatter

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