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Hardware Thread, May just have had an idea that'll save a few hundred quid in Technical; Originally Posted by CyberNerd I didn't think zraid cares what size the drive is because it just adds it to ...
  1. #16


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    Quote Originally Posted by CyberNerd View Post
    I didn't think zraid cares what size the drive is because it just adds it to the pool, unlike traditional raid systems.
    Ideally you would want to keep all drives in a vdev the same, not just for optimal performance, but also because your vdev will be limited by the size of the smallest drive if you used disks with different capacities.

    Unlike traditional file systems, which reside on single devices and thus require a volume manager to use more than one device, ZFS filesystems are built on top of virtual storage pools called zpools. A zpool is constructed of virtual devices (vdevs), which are themselves constructed of block devices: files, hard drive partitions, or entire drives, with the last being the recommended usage. Block devices within a vdev may be configured in different ways, depending on needs and space available: non-redundantly (similar to RAID 0), as a mirror (RAID 1) of two or more devices, as a RAID-Z (similar to RAID-5) group of three or more devices, or as a RAID-Z2 (similar to RAID-6) group of four or more devices. In July 2009, triple-parity RAID-Z3 was added to OpenSolaris.

    Thus, a zpool (ZFS storage pool) is vaguely similar to a computer's RAM. The total RAM pool capacity depends on the number of RAM memory sticks and the size of each stick. Likewise, a zpool consists of one or more vdevs. Each vdev can be viewed as a group of hard disks (or partitions, or files, etc.). Each vdev should have redundancy because if a vdev is lost, then the whole zpool is lost. Thus, each vdev should be configured as RAID-Z1, RAID-Z2, mirror, etc. It is not possible to change the number of drives in an existing vdev (Block Pointer Rewrite will allow this, and also allow defragmentation), but it is always possible to increase storage capacity by adding a new vdev to a zpool. It is possible to swap a drive to a larger drive and resilver (repair) the zpool. If this procedure is repeated for every disk in a vdev, then the zpool will grow in capacity when the last drive is resilvered. A vdev will have the same capacity as the smallest drive in the group. For instance, a vdev consisting of three 500 GB and one 700 GB drive, will have a capacity of 4 x 500 GB.

    In addition, pools can have hot spares to compensate for failing disks. When mirroring, block devices can be grouped according to physical chassis, so that the filesystem can continue in the case of the failure of an entire chassis. (Source)
    Here's what a hypothetical 30TB zpool could look like (please correct me if I am wrong )...

    Code:
    +---------------------------------------------------------+
    | +-------++-------++-------++-------++-------+           |
    | |       ||       ||       ||       ||       |           |
    | |       ||       ||       ||       ||       |   16TB    |
    | | 4.0TB || 4.0TB || 4.0TB || 4.0TB || 4.0TB |  RAID-Z1  |
    | |       ||       ||       ||       ||       |   vdev    |
    | |       ||       ||       ||       ||       |           |   30TB
    | +-------++-------++-------++-------++-------+           |   zpool
    | +-------++-------++-------++-------++-------+           |
    | |       ||       ||       ||       ||       |           |
    | |       ||       ||       ||       ||       |   8.0TB   |
    | | 2.0TB || 2.0TB || 2.0TB || 2.0TB || 2.0TB |  RAID-Z1  |
    | |       ||       ||       ||       ||       |   vdev    |
    | |       ||       ||       ||       ||       |           |
    | +-------++-------++-------++-------++-------+           |
    +---------------------------------------------------------+

  2. Thanks to Arthur from:

    CyberNerd (19th May 2012)

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    Bearing in mind that in most cases the MTBF is purely another hypothetical statistic as clearly it isn't possible to actually test an HDD for these periods unless you happen to own a TARDIS.
    Its a bit like the manufacturer claiming that the Triton Cell of my Smart will protect me in the event of a 70mph head on collision, the fact that my internal organs will probably emerge from most orifice's doesn't come into it, likewise you really won't know if that economy drive is going to run for 8 years until it does or will it simply expire after 13 months along with all of your data?

    The enterprise disks run a lot cooler, vibrate less, suffer from fewer errors as a result, that in itself is why you should buy them and entrust your data to them.
    I have used Enterprise quality SATA in lots of HP Caddies without any issues.
    Also, checkout the Netgear ReadyNAS list of approved HDDs this lists a whole bunch of drives that meet their stringent warranty requirements and as such should be more than capable of the requirements of the OP's proposed use.

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    Quote Originally Posted by localzuk View Post
    Ok, firstly standard SATA drives have a lower 'MTBF' than enterprise class drives. If you want to maintain 'hot swap' capability, then you'd need to buy hot swap capable drives. 1TB hotswap drives aren't cheap basically. Cheapest I can find is about £180.

    If it were me, I'd be going for the Fujitsu ones for piece of mind. Although, if it were me I'd be running a mile and screaming before I bought Fujitsu...
    Nothing wrong with recent Fujitsu equipment, Fuj Siemens are a bit more questionable. Recent Fujtisu equipment comes with a free 3 yr on-site next day warranty for all education customers, bought through an appropriate vendor that is.

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