On Nov 18, 2015, at 1:01 PM, John R Pierce <pierce at hogranch.com> wrote:> > On 11/18/2015 11:55 AM, Warren Young wrote: >> It?s rather annoying to buy a NAS, then later realize you need to buy*another* NAS as a mirror in case the first one roaches itself. Isn?t that what redundant storage is supposed to avoid? > > > no, RAID is purely availability when faced with single or double drive failure, nothing else. classic raid is most certainly NOT about data integrity, as the raid stripes aren't checksummed, they assume hardware data integrity.I knew I?d get some kind of lecture like that. Look, I know RAID/ZFS is not a backup. My point is simply that if you need to keep a mirror of your file server just in case it roaches itself, what you have there is dual redundancy, not a backup. You need an offline backup *on top* of that, for the same reason that all hot mirrors are not backups. My point is that unreliable NAS/RAID systems *require* this dual redundancy, whereas a reliable system only needs normal backups, that being the sort where you rarely go back and pull more than a few files at a time.
On 11/18/2015 1:25 PM, Warren Young wrote:> My point is that unreliable NAS/RAID systems*require* this dual redundancy, whereas a reliable system only needs normal backups, that being the sort where you rarely go back and pull more than a few files at a time.well, at the sub $1000 price point of the typical SOHO NAS box, you're not going to find high 'reliable' systems, with redundant power supplies, dual storage controllers, and everything else that goes along with 'high availability'. even my fairly well built $7000-ish 2U servers in my development lab, if the motherboard or a CPU chip fails? they are offline until repaired, if they were mission critical, I'd need pairs of everything.. if a network switch fails? yeah, I didn't implement fully redundant multipath networking either. the /really/ hard one when rolling your own highly redundant systems with high data integrity needed for things like transactional database servers, is implementing redundant storage controllers with shared writeback cache... you pretty much have to get into EMC class hardware for this level of reliability with data integrity and performance. and thats /really/ expensive stuff. -- john r pierce, recycling bits in santa cruz
Warren Young wrote:> On Nov 18, 2015, at 1:01 PM, John R Pierce <pierce at hogranch.com> wrote: >> >> On 11/18/2015 11:55 AM, Warren Young wrote: >>> It?s rather annoying to buy a NAS, then later realize you need to >>> buy*another* NAS as a mirror in case the first one roaches itself. >>> Isn?t that what redundant storage is supposed to avoid? >> >> no, RAID is purely availability when faced with single or double drive >> failure, nothing else. classic raid is most certainly NOT about data >> integrity, as the raid stripes aren't checksummed, they assume hardware >> data integrity. > > I knew I?d get some kind of lecture like that. > > Look, I know RAID/ZFS is not a backup. My point is simply that if you > need to keep a mirror of your file server just in case it roaches itself, > what you have there is dual redundancy, not a backup. You need an offline > backup *on top* of that, for the same reason that all hot mirrors are not > backups.<smip> Which is why, for home, I went to MicroCenter and bought, for about $30 USD, a hot swap drive bay that fits in my mid-sized tower, and a 2TB drive. Doesn't even need a sled.... mark
On Nov 18, 2015, at 2:58 PM, m.roth at 5-cent.us wrote:> >>> On 11/18/2015 11:55 AM, Warren Young wrote: >>>> It?s rather annoying to buy a NAS, then later realize you need to >>>> buy*another* NAS as a mirror in case the first one roaches itself. >>> > Which is why, for home, I went to MicroCenter and bought, for about $30 > USD, a hot swap drive bay that fits in my mid-sized tower, and a 2TB > drive. Doesn't even need a sled?.That?s great if your volume fits onto a single hard disk. I use 4-5 bay NASes because I have more than 8 TiB under management, and want volume level redundancy on top of that. That means 4+ 4 TiB disks, at minimum, which means I need another like-kind NAS to backstop the first.