[ale] ISCSI array on virtual machine

[Jim Kinney]

I have a large drive array for my department. I use LVM to carve it up. I
leave a huge chunk unallocated so I can extend logical partitions as
required. That dodges the need to shrink existing partitions and allows XFS
as filesystem.
On Apr 28, 2016 3:27 AM, "Todor Fassl" <fassl.tod at gmail.com> wrote:

> With respect to your question about using LVM ... I guess that was sort of
> my original question. If I just allocate the whole 8T to one big partition,
> I'd have no reason to use LVM. But I can see the need to use LVM if I
> continue with the scheme where I split the drive into partitions for
> faculty, grads, and staff.
>
> On 04/27/2016 02:27 PM, Jim Kinney wrote:
>
>> If you need de-dup, ZFS is the only choice and be ready to throw a lot
>> of RAM into the server so it can do it's job. I was looking at dedupe
>> on 80TB and the RAM hit was 250GB.
>> XFS vs EXT4.
>> XFS is the better choice.
>> XFS does everything EXT4 does except shrink. It was designed for (then
>> very) large files (video) and works quite well with smaller files. It's
>> as fast as EXT4 but will handle larger files and many, many more of
>> them. I want to say exabytes but not certain. Petabytes are OK
>> filesystem sizes with XFS right now. I have no experience with a
>> filesystem of that size but I expect there to be some level of metadata
>> performance hit.
>> If there's the slightest chance of a need to shrink a partition (You
>> _are_ using LVM, right?) then XFS will bite you and require relocation,
>> tear down, rebuild, relocation. Not a fun process.
>> A while back, an install onto a 24 TB RAID6 array refused to budge
>> using EXT4. While EXT4 is supposed to address that kind of size, it had
>> bugs and unimplemented plans for expansion features that were blockers.
>> I used XFS instead and never looked back. XFS has a very complete
>> toolset for maintenance/repair needs.
>> On Wed, 2016-04-27 at 13:54 -0500, Todor Fassl wrote:
>>
>>> I need to setup a new file server on a virtual machine with an
>>> attached
>>> ISCSI array. Two things I am obsessing over -- 1. Which file system
>>> to
>>> use and 2. Partitioning scheme.
>>>
>>> The ISCSI array is attached to a ubuntu 16.04 virtual machine. To
>>> tell
>>> you the truth, I don't even know how that is done. I do not manage
>>> the
>>> VMware cluster.  In fact, I think the Dell technitian actually ddid
>>> that
>>> for us. It looks like a normal 8T hard drive on /dev/sdb to the
>>> virtual
>>> machine. The ISCSI array is configured for RAID6 so from what I
>>> understand, all I have to do is choose a file system appropriate for
>>> my
>>> end user's needs. Even though the array looks like a single hard
>>> drive,
>>> I don't have to worry about software RAID or anyhthing like that.
>>>
>>> Googling shows me no clear advantage to ext4, xfs, or zfs. I haven't
>>> been able to find a page that says any one of those is an obvious
>>> choice
>>> in my situation. I have about 150 end-users with nfs mounted home
>>> directories. We also have a handful of people using Windows so the
>>> file
>>> server will have samba installed. It's a pretty good mix of large
>>> files
>>> and small files since different users are doing drastically
>>> different
>>> things. There are users who never do anything but read email and
>>> browse
>>> the web and others doing fluid dynamic simulations on small
>>> supercomputers.
>>>
>>> Secondthing I've been going back and forth on in my own mind is
>>> whether
>>> to do away with seperate partitions for faculty, staff, and grad
>>> students. My co-worker says that's probably an artifact of the days
>>> when
>>> partition sizes were limited. That was before my time here. The last
>>> 2
>>> times we rebuilt our file server, we just maintained the
>>> partitioning
>>> scheme and just made the sizes  times larger. But sometimes the
>>> faculty
>>> partition got filled up while there was still plenty of space left
>>> on
>>> the grad partition. Or it might be the other way around. If we
>>> munged
>>> them all together, that wouldn't happen. The only downside I see to
>>> doing that is that if the faculty partition gets hosed, the grad
>>> partition wouldn't be effected. But that seems like a pretty
>>> arbitrary
>>> choice. We could just assign users randomly to one partition or
>>> another.
>>> When you're setting up a NAS for use by a lot of users, is it
>>> considered
>>> best practice to split it up to limit the damage from a messed up
>>> file
>>> system? I mean, hopefully, that never happens anyway, right?
>>>
>>> Right now, I've got it configured as one gigantic 8T ext4 partition.
>>> But
>>> we won't be going live with it until the end of May so I have plenty
>>> of
>>> time to completely rebuild it.
>>>
>>>
>>>
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>>
> --
> Todd
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