As said before, if more than two disks in a RAID-6 array die, the array is unrecoverable.
However, three simultaneous disk failures are quite an unlikely event: it might very well be a case of a faulty enclosure, backplane and/or controller.
You should try removing and re-inserting the disks, replacing the controller and/or the enclosure, and even putting ...
A 10-20$ "hardware" RAID card is nothing more than a opaque, binary driver blob running a crap software-only RAID implementation. Stay well away from it.
A 200$ RAID card offer proper hardware support (ie: a RoC running another opaque, binary blob which is better and does not run on the main host CPU). I suggest to stay away from these cards also because, ...
You actually part answered this in your question.
The lowest form of RAID is RAID 1. RAID 0 was added well after RAID was defined (can't find reference to a date for this though)
The 0 in RAID 0 is used to signify that actually it isn't considered redundant. Think of it as more True/False where 0 is False.
Generally no, this is not a good thing to do.
Let your underlying storage do the RAID and don't add software RAID unless you have a compelling edge case, and even then you probably should reconsider your design. It will increase overhead, decrease performance, and not add a whole lot of benefit.
Software RAID has its place. That place isn't on top of ...
Yes, a functional checksummed filesystem is a very good thing. However, the real motivation is not to be found into the mythical "bitrot" which, while does happen, is very rare. Rather, the main advantage is that such a filesystem provide and end-to-end data checksum, actively protecting you by erroneous disk behavior as misdirected writes and data ...
This is not really an answer as there is not enough context to give the exact cause, but it is a description of how I managed to track this when it happened to me.
I noticed my jbd2/md0-8 kept showing up at the top of iotop. I looked in /sys/kernel/debug/tracing/events/jbd2 to see what options there are to determine what jbd2 was doing.
NOTE-1: To see ...
You're not done with performance tuning yet.
<driver name='qemu' type='raw' cache='writethrough' io='native'/>
First is which I/O mechanism to use.
QEMU has two asynchronous I/O mechanisms: POSIX AIO emulation using a pool of worker threads and native Linux AIO.
Set either io='native' or io='threads' in your XML to benchmark each of these.
Or does everything still carry on as software raid automatically until the
faulty raid card is replaced?
How would that work? Would the software magically bypass the hardware raid, which acts as disk controller? Not only does the OS not see the disks, they are actually physically attached to the hardware raid controller. If the controller fails, then ...
You don't give any details on the server type, RAID controller type or anything specific.
Try turning everything off for 10 minutes... Remove power from the server. Let the drives spin down.
Power the server back on and see if the RAID controller re-recognizes the drives and is able to boot.
You can cancel an array resync in progress using the following sequence of commands (as root):
echo frozen > /sys/block/md0/md/sync_action
echo none > /sys/block/md0/md/resync_start
echo idle > /sys/block/md0/md/sync_action
Note that this may leave your array in an inconsistent state. Don't do this unless you're sure the array is in good shape, ...
As stated in the comment, RAID6 can sustain up to two disk failures; if a third disk fails, your array is toast.
The most obvious thing is to restore from backup. If this is not possible and at least one of the failed disk is still readable (albeit with read errors), you can try to do a block-level copy of each failed disk on another, healty disk (eg: via ...
How does the RA setting get passed down the virtual block device chain?
It depends. Let's assume you are inside Xen domU and have RA=256. Your /dev/xvda1 is actual LV on the dom0 visible under /dev/dm1. So you have RA(domU(/dev/xvda1)) = 256 and RA(dom0(/dev/dm1)) = 512 . It will have such effect that dom0 kernel will access /dev/dm1 with another RA than ...
Based on your problem description your issue isn't so much the server as the storage.
You want a reliable, robust filesystem like ZFS that's designed to handle large storage capacity well, and has built-in management capabilities to make that end of the system easier to manage.
As was mentioned in the comments, I'd go with ZFS for the storage pool (probably ...
1) How can I detect if grub is installed in /dev/sdb's MBR?
You can issue:
# dd if=/dev/sda bs=512 count=1 | xxd | grep -i grub
1+0 records in
1+0 records out
512 bytes (512 B) copied, 0.00103986 s, 492 kB/s
0000180: 4752 5542 2000 4765 6f6d 0048 6172 6420 GRUB .Geom.Hard
2) Is it safe to run grub-install in /dev/sdb? Is this the correct way of making ...
RAID is just a name with a meaning that changed over time.
The important part is that the underlying technology and mechanisms are the same for the RAID levels, so you use the same controller (or piece of software, e.g. mdraid) to achieve all RAID levels.
the Raid Controller fails
I'm an electronics engineer, so my mental picture of the word "fail" may vary from a software engineers'... I mean, how often do you guys put on safety glasses for debugging?
If your RAID controller board has any kind of hardware failure which involves shorted MOSFETs, tantalum capacitors bursting into fireballs, power supply ...
In general, it doesn't make sense to do this most of the time.
However, there are a handful of special cases where it does make sense (this is not an exhaustive list, just the stuff I can think of):
The admin knew how to set up software RAID arrays on Linux, but not on VMWare, so he set it up where he knew he could properly manage it. This would be my ...
Patches for mdraid RAID 1 and 10 support for TRIM went up about a year ago.
You can test your kernel's support by mounting the filesystem with the discard option (which enables automatic TRIM). If it is supported, you'll see a message in syslog or dmesg like the following:
EXT4-fs (md1): re-mounted. Opts: discard,data=ordered
Otherwise you would get this:
Go ZFS. Seriously. It's so much better compared to hardware RAID, and reason is simple: It uses variable size strips so parity RAID modes (Z1 & Z2, RAID5 & RAID6) equivalents are performing @ RAID10 level still being extremely cost-efficient. + you can use flash cache (ZIL, L2ARC etc) running @ dedicated set of PCIe lanes.
You can use grub-emu to see the menu that grub will show when the machine next reboots.
$ sudo apt-get install grub-emu
$ sudo grub-emu
On my desktop machine the menu was displayed as expected, although if I actually pretended to boot a kernel I got a "no such device" error. I think that is expected behaviour.
On my DigitalOcean VPS no entries were ...
Software RAID is really intended for use when you have multiple physical disks without an accompanying RAID capable HDD controller. If you have hardware RAID then I'm hard pressed to see where software RAID in addition to hardware RAID provides any benefit. To the contrary, software RAID on top of hardware RAID probably induces a performance hit on the disk ...
It depends on the drives, the disk controller, the type of SSD, the RAID implementation, the Operating System(s) involved, the server, monitoring ability, whether you have out-of-band access to the server, etc.
Edit: you'll be on Linux + KVM.
Envision a drive failure of a hardware RAID solution that takes out one disk. You receive an alert and have the ...
Do not attempt to mount directly the device ! You need to mount a partition of it.
For example, this is wrong when you do:
mount /dev/sda /mnt
What you should do is:
mount /dev/sda3 /mnt
The system need the meta-data enclosed in the partition to know what to do with it. If you mount directly the device, these meta-data are missing and the mount will ...
I had a Seagate HDD that started failing checksums each time I was running zfs scrub. It failed after a few weeks. ZFS and Btrfs have checksums for data and metadata. ext4 has only metadata chcksums.
Only CRC errors and metadata checksum errors. Data corruption can happen.
If it has bad sectors it is not a problem. The entire disk will be "failed", but you ...
You've had a double drive failure, with one of the drives being dead for six months. With RAID5, this is irrecoverable. Replace the failed hardware and restore from backup.
Going forward, consider RAID6 with large drives like this and make sure you have monitoring in place to catch device failures so you can respond to them ASAP.
To tell the truth, it seems that LSI does not provide much details on its FastPath tech.
Anyway, some information can be gathered from the DELL docs:
from DELL PERC H710P controller brief:
Dell’s FastPath™ software feature enables the use of the second core
on our PowerPC chip to accelerate write-through I/O, which
significantly enhances SSD ...
Your SMART Current Pending Sector has value 1. This means that there is a bad sector on the disk and the drive firmware is unable to reallocate it, but you still have zero reallocated sectors count so it probably recoverable even though your drive have been running for 5 years in not very healthy environment - temperatures are up to 72 C°.
You can try ...
The measured low performance are the results of various factors:
after creation the array is entirely synched, causing the allocation of most (if not all) flash data pages on half the SSDs. This will put the SSDs in a low performance state until a secure erase / trim "frees" all/most/some pages. This explain the increased performance after an fstrim;
If you really want to use 4 disks for a RAID1 array, I suggest you to go with a 4-way RAID1 array. In this manner, should a disk fail, you continue to have tripe-protection (3-way array) without needing any rebuild.
If you really want a 3-way mirror + hot spare, you can use mdadm --manage --add-spare to add a spare to the RAID1 array. For example, lets ...