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Mounting disk images on Linux loopback device
Disk space. There's never enough. Whilst preping my Inspiron 3800 for its new 20GB Toshiba 4500 RPM disk I thought I'd play around some with disk imaging. Playing with partition images is boring, so let's spice it up!
storage  dd  disk 
yesterday by dusko
[SOLVED] iSCSI - Shared storage question / Best practices - Spiceworks
With iSCSI, the server is sharing out raw disk space and the client is responsible for file systems, etc.

With NAS, the server is sharing folders, windows-style.

Synology has a "thin-provisioning" feature which allows the box to represent the drive as larger than what's actually there. This is good for servers where it's difficult to re-size the drive after it's deployed, but the growth is slow or at least predictable so you can grow the array later. I think this is just on the iSCSI side, not the NAS side, but don't hold me to that (EDIT: for Synology I mean, not everywhere).

The NAS side and the iSCSI side are different slices of the array, by the way. Or at least, they really, really should be.
iscsi  storage  disk  hardware  server  qemu  kvm  virtualization  nas 
yesterday by dusko
How to read and iscsi volume from a flat file? - Data Storage - Spiceworks
iSCSI is a connection format, it has nothing to do with what is on the storage. What you have are filesystem images (ISOs.) Just mount them like you would any ISO. And you'll need whatever filesystem driver is necessary to read whatever filesystem is on the drive image.

One of the advantages of a NAS recovery as opposed to a SAN one is that when a NAS is recovered, what you have are files. When a SAN is recovered, what you have are file systems. Much harder to deal with recovering from a SAN than a NAS, vastly more complex. A SAN really is not designed to be backed up directly, just as disks are not. You back up from a higher level, typically, not from the SAN level. But a NAS is already at that higher level. So backups of a NAS, and the state of recovered data, is much more usable.
iscsi  storage  hardware  disk  qemu  kvm  virtualization  backup  disasterrecovery 
yesterday by dusko
linux - Free space in unmounted partition - Unix & Linux Stack Exchange
There is no general way for that, but there is a way which works in most cases.

The reason, why there is no general way for that, that also the kernel doesn't know it. To know it, first it would need to analyze the partition.

Without mounting the partition, the kernel knows only its existence, but no more. Essentially, it is a line of blocks with random data. The kernel knows, where is it and how to access, but doesn't know, what to do with it.

However, there are also user-space tools which can analyze the content of a filesystem, without mounting them. As all the filesystems have very different data structures, to handle them you need different tools.

In the case of ext2/3/4, it is

# dumpe2fs /dev/your_root|grep '^Free blocks'
dumpe2fs 1.42.13 (17-May-2015)
Free blocks: 5721580
iscsi  storage  hardware  disk  server 
yesterday by dusko
NFS vs iSCSI, fight! (your thoughts on performance) - sysadmin
There have been rigorous empirical studies on this. There's no significant intrinsic difference in performance between iSCSI and NFS.

Use whichever implementations seem most stable, most readily administrated, and best-performant as compared to the others at your disposal.

iSCSI is faster at both, but NFS comes at a close second. NFS was easier for me to deploy, and I can use it with Proxmox for backups, that is why I went with it.
iscsi  storage  hardware  disk  server  sysadmin  nas  performance 
yesterday by dusko
What is a block device? - Unix & Linux Stack Exchange
A Block Special File or block device is (http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_79):

A file that refers to a device. A block special file is normally distinguished from a character special file by providing access to the device in a manner such that the hardware characteristics of the device are not visible.

The precise hardware characteristics are abstracted away by kernel- or driver-level caching. Block devices commonly represent hardware such as disk drives, but that is platform-dependent. FreeBSD doesn't have any block devices at all (https://www.freebsd.org/doc/en/books/arch-handbook/driverbasics-block.html), for example.
iscsi  disk  hardware  storage  server  sysadmin 
2 days ago by dusko
balenaEtcher - Home
A cross-platform tool for flashing images to SD cards & USB drives.
drive  bootable  USB  key  create  boot  OS  install  copy  disk  image  flash  windows  macos  linux  UI 
5 days ago by ebouchut
You Don't Want XTS — Quarrelsome
FDE is oblivious to content and format. Filesystems pick unintuitive spots on the disk to stash file chunks.

You can’t authenticate the data.

The physical device imposes rigid format constraints.

Sector-level simulated hardware crypto is a last-resort solution that protects you less than you think it does.

The “XTS” label on the tin doesn’t signify powerful, advanced crypto. If you see it used for something other than simulated hardware crypto, watch out.
encryption  security  disk 
12 days ago by djbl
This can not be stressed strongly enough - There is never a case when RAID5 is the.... - Hacker News
halfcat on Sept 12, 2014

This can not be stressed strongly enough. There is never a case when RAID5 is the best choice, ever [1]. There are cases where RAID0 is mathematically proven more reliable than RAID5 [2]. RAID5 should never be used for anything where you value keeping your data. I am not exaggerating when I say that very often, your data is safer on a single hard drive than it is on a RAID5 array. Please let that sink in.

The problem is that once a drive fails, during the rebuild, if any of the surviving drives experience an unrecoverable read error (URE), the entire array will fail. On consumer-grade SATA drives that have a URE rate of 1 in 10^14, that means if the data on the surviving drives totals 12TB, the probability of the array failing rebuild is close to 100%. Enterprise SAS drives are typically rated 1 URE in 10^15, so you improve your chances ten-fold. Still an avoidable risk.

[1] http://www.smbitjournal.com/2012/11/choosing-a-raid-level-by-drive-count/
[2] http://www.smbitjournal.com/2012/05/when-no-redundancy-is-more-reliable/
raid  server  hardware  sysadmin  backup  disasterrecovery  disk 
14 days ago by dusko

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