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• Distributed storage and computing

  - by Tim van Elteren

  Dear Serverfault community, After researching a number of distributed file systems for deployment in a production environment with the main purpose of performing both batch and real-time distributed computing I've identified the following list as potential candidates, mainly on maturity, license and support: Ceph Lustre GlusterFS HDFS FhGFS MooseFS XtreemFS The key properties that our system should exhibit: an open source, liberally licensed, yet production ready, e.g. a mature, reliable, community and commercially supported solution; ability to run on commodity hardware, preferably be designed for it; provide high availability of the data with the most focus on reads; high scalability, so operation over multiple data centres, possibly on a global scale; removal of single points of failure with the use of replication and distribution of (meta-)data, e.g. provide fault-tolerance. The sensitivity points that were identified, and resulted in the following questions, are: transparency to the processing layer / application with respect to data locality, e.g. know where data is physically located on a server level, mainly for resource allocation and fast processing, high performance, how can this be accomplished? Do you from experience know what solutions provide this transparency and to what extent? posix compliance, or conformance, is mentioned on the wiki pages of most of the above listed solutions. The question here mainly is, how relevant is support for the posix standard? Hadoop for example isn't posix compliant by design, what are the pro's and con's? what about the difference between synchronous and asynchronous opeartion of a distributed file system. Though a synchronous distributed file system has the preference because of reliability it also imposes certain limitations with respect to scalability. What would be, from your expertise, the way to go on this? I'm looking forward to your replies. Thanks in advance! :) With kind regards, Tim van Elteren

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• 150 TB and growing, but how to grow?

  - by seandavi

  My group currently has two largish storage servers, both NAS running debian linux. The first is an all-in-one 24-disk (SATA) server that is several years old. We have two hardware RAIDS set up on it with LVM over those. The second server is 64 disks divided over 4 enclosures, each a hardware RAID 6, connected via external SAS. We use XFS with LVM over that to create 100TB useable storage. All of this works pretty well, but we are outgrowing these systems. Having build two such servers and still growing, we want to build something that allows us more flexibility in terms of future growth, backup options, that behaves better under disk failure (checking the larger filesystem can take a day or more), and can stand up in a heavily concurrent environment (think small computer cluster). We do not have system administration support, so we administer all of this ourselves (we are a genomics lab). So, what we seek is a relatively low-cost, acceptable performance storage solution that will allow future growth and flexible configuration (think ZFS with different pools having different operating characteristics). We are probably outside the realm of a single NAS. We have been thinking about a combination of ZFS (on openindiana, for example) or btrfs per server with glusterfs running on top of that if we do it ourselves. What we are weighing that against is simply biting the bullet and investing in Isilon or 3Par storage solutions. Any suggestions or experiences are appreciated.

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• Replicated filesystem and EC2 MySQL

  - by El Yobo

  I'm currently investigating migrating our infrastructure over to run on Amazon's EC2 and am trying to figure out the best way to set up a MySQL service. I'm leaning towards running our own MySQL instances, rather than going with Amazon's RDS, but am still considering the best approach for performance and cost on the instance itself. In order to have persistent data, the MySQL data needs to be on an EBS volume (with some form of striped RAID, e.g. RAID0 or RAID10) to improve persistence. However, EBS IO is limited by the network interface (gigabit, so a theoretical maximum of 128 MB/s), while the ephemeral volumes have no such problem. I did see a suggestion for running two MySQL servers on an instance, with a master running on the ephemeral disk (which we would also RAID) and a slave storing changes to an EBS volume, but this has some additional overhead and complexity (two servers). What I was imagining is using some form of replicated file system such that I could have a filesystem on top of a RAID0 of ephemeral volumes to maximise performance all changes from the above immediately replicated to another RAID1 volume backed by multiple EBS volumes to ensure no data loss The advantages of this would be best possible IO performance for the DB server; no network delay in IO decreased IO on EBS volumes (as all read IO will be done on the ephemeral volumes) so decreased cost good data security, as it's backed onto redundant EBS volumes However, I haven't seen an appropriate system to replicate all changes from one volume to the other; is there a filesystem, or any other approach, which will do this? The distributed file systems, e.g. GlusterFS, DRBD etc seem to focus on replicating disks between servers, can they be set up to do what I'm interested in here? I also haven't seen anything about other's taking this approach. Do I have a solution in need of a problem here (i.e. is performance good enough, so this whole idea is redundant)? Is there some flaw in the plan?

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• Sharing storage between servers

  - by El Yobo

  I have a PHP based web application which is currently only using one webserver but will shortly be scaling up to another. In most regards this is pretty straightforward, but the application also stores a lot of files on the filesystem. It seems that there are many approaches to sharing the files between the two servers, from the very simple to the reasonably complex. These are the options that I'm aware of Simple network storage NFS SMB/CIFS Clustered filesystems Lustre GFS/GFS2 GlusterFS Hadoop DFS MogileFS What I want is for a file uploaded via one webserver be immediately available if accessed through the other. The data is extremely important and absolutely cannot be lost, so whatever is implemented needs to a) never lose data and b) have very high availability (as good as, or better, than a local filesystem). It seems like the clustered filesystems will also provide faster data access than local storage (for large files) but that isn't of vita importance at the moment. What would you recommend? Do you have any suggestions to add or anything specifically to look out for with the above options? Any suggestions on how to manage backup of data on the clustered filesystems?

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• Postfix MySql Dovecot - SMTP Authentication Failure

  - by borncamp

  Hello I have a Postfix setup with Dovecot and MySql. The server is running Debian Squeeze. The MySql server is a slave that has data pushed to it from a primary (postfix) mail server(running a different os). The emails are stored on a replicated GlusterFS volume. I am able to check email using thunderbird over IMAP. However, SMTP requests fail. After turning on query logs for the MySql server I have noticed that no query statement is executed to retrieve the user information when an SMTP client tries to authenticate. I'd like to know what I'm doing wrong or what the next troubleshooting steps are. I'm about to pull my hair out. Below is some log and configuration data that I thought would be relevant. You're help is much obliged. The file /var/log/mail.log shows Oct 11 14:54:16 mailbox2 postfix/smtpd[25017]: connect from unknown[192.168.0.44] Oct 11 14:54:19 mailbox2 postfix/smtpd[25017]: warning: unknown[192.168.0.44]: SASL PLAIN authentication failed: Oct 11 14:54:25 mailbox2 postfix/smtpd[25017]: warning: unknown[192.168.0.44]: SASL LOGIN authentication failed: VXNlcm5hbWU6 Oct 11 14:55:48 mailbox2 postfix/smtpd[25017]: warning: unknown[192.168.0.44]: SASL PLAIN authentication failed: VXNlcm5hbWU6 Oct 11 14:55:54 mailbox2 postfix/smtpd[25017]: warning: unknown[192.168.0.44]: SASL LOGIN authentication failed: VXNlcm5hbWU6 Oct 11 14:55:57 mailbox2 postfix/smtpd[25017]: disconnect from unknown[192.168.0.44] This is my dovecot.conf file log_timestamp = "%Y-%m-%d %H:%M:%S " mail_location = maildir:/var/mail/virtual/%d/%n/ auth_mechanisms = plain login disable_plaintext_auth = no namespace { inbox = yes location = prefix = INBOX. separator = . type = private } passdb { args = /etc/dovecot/dovecot-mysql.conf driver = sql } protocols = imap pop3 service auth { unix_listener /var/spool/postfix/private/auth { group = postfix mode = 0660 user = postfix } unix_listener auth-master { mode = 0600 user = postfix } user = root } ssl_cert = </etc/ssl/certs/dovecot.pem ssl_key = </etc/ssl/private/dovecot.pem userdb { args = /etc/dovecot/dovecot-mysql.conf driver = sql } protocol lda { auth_socket_path = /var/run/dovecot/auth-master mail_plugins = sieve postmaster_address = [email protected] } protocol pop3 { pop3_uidl_format = %08Xu%08Xv } Here is my dovecot-mysql.conf file: connect = host=127.0.0.1 dbname=postfix user=postfix password=ffjM2MYAqQtAzRHX driver = mysql default_pass_scheme = MD5-CRYPT password_query = SELECT username AS user,password FROM mailbox WHERE username = '%u' AND active='1' user_query = SELECT CONCAT('/var/mail/virtual/', maildir) AS home, 1001 AS uid, 109 AS gid, CONCAT('*:messages=10000:bytes=',quota) as quota_rule, 'Trash:ignore' AS quota_rule2 FROM mailbox WHERE username = '%u' AND active='1' Here is my output from 'postconf -n': append_dot_mydomain = no biff = no bounce_template_file = /etc/postfix/bounce.cf broken_sasl_auth_clients = yes config_directory = /etc/postfix delay_warning_time = 0h dovecot_destination_recipient_limit = 1 inet_interfaces = all local_recipient_maps = $virtual_mailbox_maps local_transport = virtual mailbox_command = procmail -a "$EXTENSION" mailbox_size_limit = 0 maximal_queue_lifetime = 1d message_size_limit = 25600000 mydestination = mailbox2.cws.net, debian.local.cws.net, localhost.local.cws.net, localhost myhostname = mailbox2.cws.net mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 172.18.0.119 63.164.138.3 myorigin = /etc/mailname proxy_read_maps = $local_recipient_maps $mydestination $virtual_alias_maps $virtual_alias_domains $virtual_mailbox_maps $virtual_mailbox_domains $relay_recipient_maps $relay_domains $canonical_maps $sender_canonical_maps $recipient_canonical_maps $relocated_maps $transport_maps $mynetworks $virtual_mailbox_limit_maps readme_directory = no recipient_delimiter = + relay_domains = relayhost = smtp_connect_timeout = 10 smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU) smtpd_client_message_rate_limit = 50 smtpd_client_recipient_rate_limit = 500 smtpd_client_restrictions = permit_sasl_authenticated, permit_mynetworks smtpd_delay_reject = yes smtpd_discard_ehlo_keyword_address_maps = hash:/etc/postfix/discard_ehlo smtpd_helo_required = yes smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname, permit smtpd_recipient_restrictions = permit_mynetworks,permit_sasl_authenticated,reject_unauth_destination smtpd_sasl_auth_enable = yes smtpd_sasl_authenticated_header = yes smtpd_sasl_path = private/auth smtpd_sasl_security_options = noanonymous smtpd_sasl_tls_security_options = $smtpd_sasl_security_options smtpd_sasl_type = dovecot smtpd_sender_restrictions = permit_mynetworks, reject_non_fqdn_sender, reject_unknown_sender_domain, permit smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache smtpd_use_tls = yes transport_maps = hash:/etc/postfix/transport virtual_alias_maps = proxy:mysql:/etc/postfix/sql/mysql_virtual_alias_maps.cf, proxy:mysql:/etc/postfix/sql/mysql_virtual_alias_domain_maps.cf, proxy:mysql:/etc/postfix/sql/mysql_virtual_alias_domain_catchall_maps.cf virtual_gid_maps = static:1001 virtual_mailbox_base = /var/mail/virtual/ virtual_mailbox_domains = proxy:mysql:/etc/postfix/sql/mysql_virtual_domains_maps.cf virtual_mailbox_maps = proxy:mysql:/etc/postfix/sql/mysql_virtual_mailbox_maps.cf, proxy:mysql:/etc/postfix/sql/mysql_virtual_alias_domain_mailbox_maps.cf virtual_transport = dovecot virtual_uid_maps = static:1001

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• Cross-platform distributed fault-tolerant (disconnected operation/local cache) filesystem

  - by Adrian Frühwirth

  We are facing a design "challenge" where we are required to set up a storage solution with the following properties: What we need HA a scalable storage backend offline/disconnected operation on the client to account for network outages cross-platform access client-side access from certainly Windows (probably XP upwards), possibly Linux backend integrates with AD/LDAP (permission management (user/group management, ...)) should work reasonably well over slow WAN-links Another problem is that we don't really know all possible use cases here, if people need to be able to have concurrent access to shared files or if they will only be accessing their own files, so a possible solution needs to account for concurrent access and how conflict management would look in this case from a user's point of view. This two years old blog posts sums up the impression that I have been getting during the last couple of days of research, that there are lots of current übercool projects implementing (non-Windows) clustered petabyte-capable blob-storage solutions but that there is none that supports disconnected operation nicely and natively, but I am hoping that we have missed an obvious solution. What we have tried OpenAFS We figured that we want a distributed network filesystem with a local cache and tested OpenAFS (which, as the only currently "stable" DFS supporting disconnected operation, seemed the way to go) for a week but there are several problems with it: it's a real pain to set up there are no official RHEL/CentOS packages the package of the current stable version 1.6.5.1 from elrepo randomly kernel panics on fresh installs, this is an absolute no-go Windows support (including the required Kerberos packages) is mystical. The current client for the 1.6 branch does not run on Windows 8, the current client for the 1.7 does but it just randomly crashes. After that experience we didn't even bother testing on XP and Windows 7. Suffice to say, we couldn't get it working and the whole setup has been so unstable and complicated to setup that it's just not an option for production. Samba + Unison Since OpenAFS was a complete disaster and no other DFS seems to support disconnected operation we went for a simpler idea that would sync files against a Samba server using Unison. This has the following advantages: Samba integrates with ADs; it's a pain but can be done. Samba solves the problem of remotely accessing the storage from Windows but introduces another SPOF and does not address the actual storage problem. We could probably stick any clustered FS underneath Samba, but that means we need a HA Samba setup on top of that to maintain HA which probably adds a lot of additional complexity. I vaguely remember trying to implement redundancy with Samba before and I could not silently failover between servers. Even when online, you are working with local files which will result in more conflicts than would be necessary if a local cache were only touched when disconnected It's not automatic. We cannot expect users to manually sync their files using the (functional, but not-so-pretty) GTK GUI on a regular basis. I attempted to semi-automate the process using the Windows task scheduler, but you cannot really do it in a satisfactory way. On top of that, the way Unison works makes syncing against Samba a costly operation, so I am afraid that it just doesn't scale very well or even at all. Samba + "Offline Files" After that we became a little desparate and gave Windows "offline files" a chance. We figured that having something that is inbuilt into the OS would reduce administrative efforts, helps blaming someone else when it's not working properly and should just work since people have been using this for years. Right? Wrong. We really wanted it to work, but it just doesn't. 30 minutes of copying files around and unplugging network cables/disabling network interfaces left us with (silent! there is only a tiny notification in Windows explorer in the statusbar, which doesn't even open Sync Center if you click on it!) undeletable files on the server (!) and conflicts that should not even be conflicts. In the end, we had one successful sync of a tiny text file, everything else just exploded horribly. Beyond that, there are other problems: Microsoft admits that "offline files" in Windows XP cannot cope with "large files" and therefore does not cache/sync them at all which would mean those files become unavailable if the connection drop In Windows 7 the feature is only available in the Professional/Ultimate/Enterprise editions. Summary Unless there is another fault-tolerant DFS that supports Windows natively I assume that stacking a HA Samba cluster on top of something like GlusterFS/Lustre/whatnot is the only option, but I hope that I am wrong here. How do other companies allow fault-tolerant network access to redundant storage in a heterogeneous environment with Windows?

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